Prepare to see a very rare sight on the Metropolitan line this coming August Bank Holiday, with a special locomotive tour taking place.

It’s all part of the 50th anniversary of the Buckinghamshire Railway Centre near Aylesbury, and to mark the event, London Underground have given permission for a special trip to take place.

On both 25th and 26th August, UK Railtours will run trips from Marylebone mainline station, and rather than heading up via Chiltern Railway’s mainline tracks, they will be allowed to cross over onto the Metropolitan line and head out via Harrow on the Hill and Amersham.

From there, they leave the tube map as the train heads out towards Great Missenden, Wendover, and Aylesbury before going onto freight-only single-track towards the neatly restored wayside station of Quainton Road, and the railway museum.

They take a second trip via the little-used Watford North Curve to head through Croxley to the terminus at Watford, back to the museum, then head back to London.

Loco-hauled railtours in and out of London Marylebone are relatively rare in themselves, but then seeing them on the Met line tracks is even rarer.

The exact timetable will be available about a week before the Bank Holiday, but the trains will leave Marylebone just after 10am each morning, and return just before 6pm in the evening.

You can be on the train as well – tickets are available here, or use the opportunity to see a rare sight by watching from the sidelines.

Subject to availability, the locomotives will be a Class 33 at one end of the train and a pair of Class 20s at the other.

The carriages will be their restored London Transport livery 4TC Unit, and with a bit of luck, the Class 20 locomotives may be the London Transport livery units as well.

Interestingly, their T&C’s warn that the train toilets will be out of use while the trains are on London Underground tracks.