The station building opened in 1907 but closed in 1914 (along with its City & South London Railway equivalent), with access to the Underground station being made through the third, shared, entrance within the mainline station itself. Whilst the CSLR building was demolished in the 1930s, this structure was retained for use in providing ventilation to the platforms below.

By 2018, even this building was surviving on borrowed time; the space being required for a further expansion of the mainline station, in order to accommodate the High Speed 2 rail link.

The former entrance was bricked up upon the building’s closure, with tiling of a similar colouring to the Leslie Green originals masking the filled-in space. The un-tiled middle of this was used for displaying advertisement posters.

Whilst the loss of a Leslie Green-designed structure is a shame, the building is not in terribly good condition, and better examples can be seen elsewhere on the Underground network.

A large fan and its associated ducting takes up much of the internal space within the building.

The semi-circular windows high up on the building still allow in a reasonable amount of daylight.

Some remnants of the former interior tiling remains; albeit, now painted over.

This staircase formed the top of the emergency stairs down to platform level originally; access is now sealed off, although the imprint of where the stairs continued can be seen on the right-hand wall, to the right of the yellow steel steps.

Further traces of original tiling can be seen at the front of the building.

Once underground, our group divided into several smaller groups. I started by exploring the newest part of the disused section - the ventilation shaft constructed in the 1960s for the Victoria line. The shaft starts alongside the former lift access that connected with the mainline booking hall. Prior to the ventilation shaft construction, there would have been a right-angled corner here.

This diagram, located within one of the empty lift shafts, shows the position of the ventilation shaft (coloured in a darker shade of mauve to the rest of the passageways) in relation to the Victoria line and Northern line’s eastbound Bank Branch - the former CSLR.

The join between old and new is apparent by the abrupt change from tiled and rendered walls to bare cast iron tunnel segments.

On the opposite side, the old tunnel rings have been revealed (right), alongside the newer (left) rings.

Looking back the other way reveals how the floor was lowered as another part of the ventilation shaft construction. The blocked-off facing wall leads to an equipment room.

Peering through the window in this door reveals that the area has received extensive modernisation in comparison to the rest of the area.

The first section of the ventilation shaft is lined in concrete. Here, another equipment room is seen - this one is involved with the Northern line Automatic Train Operation.

A view taken slightly further along the shaft, and looking back in the direction of the above photograph.

The concrete gives way to traditional cast iron tunneling segments.

Towards the end of the shaft, the tunnel takes a sharp curve to the right, in order to bring it into alignment with the Victoria line platforms below.

A rather atmospheric view looking back towards the concrete section.

In places, stalactites were seen to be forming through gaps in the tunnel rings.

The individual segments used in producing the tunnel rings make for comment in themselves - this London Transport Executive-branded segment, for example, was made at Stanton Ironworks, near Ilkeston, Derbyshire.

This segment used in the ceiling of that particular tunnel ring carries the manufacturing date of the 26th February 1966. This too is a Stanton product, although it carries the slightly later branding of Stanton & Staveley.

This segment, towards the end of the shaft, was manufactured by HW & Co, and carries the production date of the 11th January 1965.

This short section is of noticeably narrower diameter (seven foot, in comparison to the twelve foot diameter of the rest of the iron section) as it was not intended for use as ventilation; it being beyond the Victoria line platforms. Instead, this tunnel is solely intended for access.

Back in the ventilation shaft, the Victoria line could be glimpsed through grilles below the narrow catwalks of the shaft. An interesting phenomenon experienced was that much cooler air entered the shaft from the piston effect created by southbound trains compared to northbound trains, where the air dissipated was warmer.

The grilles were offset to the left or the right in the shaft, depending on whether they served the northbound or southbound platforms.

Some of the tunnel segments were older than the majority - for example, this one carried the 17th November 1958 as its manufacturing date.

We then headed back to the former lift shaft area. As with the other Yerkes’ station lifts, a one-way system was in place that enabled people to enter the lifts through one set of doors and exit using the other. The connecting passage from the back of the lifts (where the ventilation shaft now attaches) into the main corridor was home to a series of posters dating from when the area last saw public use. This poster advertised an air display at North Weald Air Field - Epping is shown in brackets below as the connection to North Weald station at the time was by changing at Epping on the Central line.

This poster, located between two of the lift doorways, advertises British Rail Inter-City services, featuring references to Liverpool and Manchester.

The remnants of another BR poster survive behind modern cabling - this appears to advertise a Sleeper service.

Standing inside the disused lift shaft, we see that a small wall had been constructed along the bottom of one of the former doorways.

An attempt at an arty shot using the ladder that had been installed up the wall of the shaft. The view reminds me of a Tube tunnel, funnily enough!

The view of the lift doorways from the corridor.

The other shaft was bricked up. Only the right-hand recess ever contained a lift; the left-hand space housed the fixed emergency stairs.

This bricked-off area also led to the corridor behind the lifts - it joins up with the same modernised area seen earlier.

To the left, yet more British Rail posters were still visible, including one advertising the famous Midland Pullman service.

Another diagram assisted with orientation - we were now in the corridor that led to the Charing Cross branch platforms.

More posters survived on the other side of the corridor, including one for the Daily Express.

A poster advertising a theatre production of Alfred Hitchcock’s thriller, Psycho, was still partially extant.

For a brief length of the corridor, more equipment rooms then filled much of the available space.

The decorative blue tiled rings were in especially good, and clean, condition in this area; particularly, those above us.

The corridor widened out to its full length again, and a short flight of steps was glimpsed in the distance.

The stairs now lead nowhere; the rebuilt Euston Underground station seeing a replacement flight of stairs built over these that pass over this corridor from the Charing Cross Branch platforms.

A chunk of the wall rendering and tiling had been removed just before the steps, exposing the tunnel segments beneath.

Heading back along the corridor, past the lift shafts, a number of wooden boxes storing various pieces of equipment for track repairs could be seen along both sides.

Traces of posters were present here too.

This poster advertising bingo at the Granada Cinema in Brixton is particularly well preserved - not that its advertising capabilities will be up to much these days; the Granada was demolished in 1992.

Fragments of a poster advertising for conductors with London Transport were attached nearby.

Looking back towards the lift shafts.

This poster advertises the release of Marriage on the Rocks from 1965, which starred Frank Sinatra, Deborah Kerr and Dean Martin.

Meanwhile, this poster advertised the release of the second part of Winston Churchill’s biography, which was released in 1967. Given Down Street’s use by Churchill during the Second World War, I think that the former Prime Minister might be haunting me!

Alongside the modern storage licence for equipment, a poster for Thoroughly Modern Millie (again, dating from October 1967) can be seen.

Heading down a few steps, we came to a split in the corridor joining up with the CSLR (Bank Branch) side of the station. This offered an alternative means of passing between both railway company platforms, and latterly both branches of the Northern line. The corridor traversed above disappears into the distance in the picture below, whilst the link corridor is behind the photographer.

Turning to the left, the next corridor to visit, beckons.

The circulating area seen above is pictured from the top of the stairs.

The 1960 film, Spartacus, was advertised nearby. This corridor was the first to close, owing to the redevelopment of Euston, and the posters reflect this.

Gilbert & Sullivan’s The Yeomen of the Guard was on in theatres at the time.

Another Spartacus poster; this one, in slightly better condition than the first, was pasted opposite.

A notice warning of the then-imminent closure of this corridor was displayed; the date of the 29th April 1962 is given as the final day that it would be open.

Another helpful couple of diagrams were positioned, with the left-hand one detailing how the station looked following the rebuilding, and introduction of the Victoria line, and the right-hand one detailing the previous arrangement.

A ticket office was provided for people changing from one Underground line to the other - the different Underground rail companies requiring their own tickets until both lines became branches of the same line. Notice that the lighter blue tiles of the Charing Cross, Euston and Hampstead Railway are joined by the much darker blue (almost black) tiles of the City & South London Railway.

A little further along, another poster warning of the corridor’s closure was displayed.

Another poster in relatively intact condition advertised London’s Meeting of Track Stars at White City in June 1961.

This poster informing of the work of the Theosophical Society has also survived remarkably well.

The corridor began to curve to the left at this point, following the formation of the Charing Cross Branch that would be approaching from above.

Considerable amounts of dust obscured the posters here.

This corridor also came up against a dead end at the top of a flight of steps, and once again, the replacement stairs pass above this corridor.

A rather gloomy view taken from the top of the steps.

A raised section above the original floor allows multiple cables to divert below the corridor.

Part of this corridor is restricted by the presence of more equipment and machinery.

A poster advertising P&O cruises was visible, despite the dirt.

A poster for Dale Carnegie courses was situated at the foot of the stairs to nowhere.

This poster, advertising West Side Story, had been modified, in order to display ‘Now Showing’, instead of the original ‘From Feb 27th’; however, the alteration has, since, fallen away (it is visible at the bottom of the picture), revealing the original date. Again, this film was released in 1961.

Partially hidden behind an equipment cabinet is this poster.

An assortment of posters over the years is seen here - typically, new posters would be pasted over the old, owing to the difficulty in removing them. Again, a poster from 1961, advertising the Christopher Lee film Terror of the Tongs is in about the most intact condition.

After heading back past the ticket office and down the steps into where the corridor splits, we were ready to rejoin the modern operational station again - the door on the right-hand side at the foot of these stairs opens out at the end of the eastbound Bank Branch platform, much to the bemusement and surprise of regular commuters waiting on the platform when the door opened and several rather grubby individuals wearing high-visibility vests emerged from it!

Although the Euston tour is not as extensive as the Aldwych or Down Street tours are, I still enjoyed it immensely and am grateful to the guides, who were able to answer all questions put to them with complete ease!