LONDON's oldest surviving "underground" train, 100 years old, steamed all of 50 yards out of its Forest repair shed this week. Weighing in at 55 tonnes, Metropolitan No. 1, first steamed along the Metropolitan Railway to and from its Baker Street terminus in1898.

Rescued when it finished its working life, it became one of the "stars" of the Buckinghamshire Railway Centre. Feeling its age a bit, it was booked into Bream's Flour Mill Steam Railway Workshop for an over-winter overhaul.

This week its boiler, a massively complicated affair involving hundreds of new tubes, was "signed off" by a BR inspector as meeting main line requirements. Driving it out of the shed, and onto a low-loader for its return to the Quainton Road Station centre, was engineer Geoff Phelps who did most of the work.

Assisted mostly by colleague Phil Davies, he was also helped by his dad Dougie Phelps, Craig Morris and Mike Brimble.

"The boiler has been restored to main-line standard, so that in future the engine can be run on the Metropolitan lines again if the opportunity arises," says Flour Mill trustee Bill Parker.

Under its Swindon Railway Workshop Ltd title, the Flour Mill has previously restored four engines from York's National Railway Museum – including replicas of Stephenson's Rocket and Brunel's Iron Duke.

"This is a very high-profile job in the railway restoration world, and we hope others will follow."

Affectionately known among steam buffs as Met 1, the engine hauled trains on several historic journeys. The last locomotive constructed at the Neasdon Works, it was the first train on the Uxbridge Branch in 1904 and worked between Aylesbury and Baker Street until the 1920s.

The Metropolitan Railway was incorporated into the newly established London Passenger Transport Board in 1933.

Having hauled London Transport's last steam passenger service in 1961, it "retired" into storage in Luton. Moving to Quainton Road in 1970, it was first restored in 1986.

As well as providing excursions for railway enthusiasts on its own former line, it was a major attraction on visits to steam centres around England. Following the expiry of its boiler certification in 1994, it became a popular static exhibit.

As the only surviving Metropolitan locomotive in steam, when it gets back to Quainton Road it will be repainted in the Met livery of crimson with black and yellow lining.