22nd April 2009: quite a special day in the history of the Gloucestershire Warwickshire Railway.

That's because, exactly 25 years earlier, on Saturday 22nd April 1984, a diminutive red tank locomotive and a single blue-and-grey railway coach set off from Toddington station on a journey along 700 yards of track … and into the future.  The then Minister of Transport, the Rt Hon. Nicholas Ridley MP had just snipped the ribbon marking the re-opening of the line and was aboard that  first train.

The GWR had, earlier that year, completed purchase of the 15 miles of derelict track bed from a point south of Hunting Butts tunnel on the outskirts of Cheltenham to just north of the site of Broadway station.

If that was the 'acorn' then the 'mighty oak' is still nowhere near fully grown, a quarter of a century later. True, the GWR now operates over 10 miles from Toddington to Cheltenham Racecourse; it runs six-coach trains and operates a fleet of main line engines, including one of the largest in the country: David Shepherd's mighty 9F class 2-10-0 'Black Prince'.  But the line is still growing - it has its sights firmly set on Broadway and beyond, it has carried its millionth passenger, sold its millionth share; has a turnover of nearly £1 million and has huge scope for development and growth.

But what of that tiny tank locomotive? Where is it now?

The engine in question was a delightful Avonside 0-4-0T which was built to shunt the sidings at the Cadbury chocolate factory in Bournville, near Birmingham.  Cadburys were very proud of their locomotive fleet.  This particular engine, resplendent in red-brown 'Bournville' livery with the legend 'Cadbury Bournville No. 1' picked out in gold leaf on the tank side, was immaculately turned out as were the rest of the locomotives.  Those were the days when chocolate and cocoa travelled by train to destinations all over the UK - long before the days of motorways and juggernaut road transporters.  Cadburys ceased using rail transport in 1976.

Cadbury No. 1 was completed in 1925 at the Avonside Engine Company in Bristol, as works number 1977; one of four similar locomotives supplied to Cadbury.  It operated at Bournville until 1963 when it was sold to the Dowty Railway Preservation Society whose base was at Ashchurch in Gloucestershire, on a site owned by Dowty Mining. In 1982 the Society was given notice to quit as the site was to be redeveloped. The following year, agreement was reached to move the 10 miles to Toddington, and the standard-gauge rolling stock, including Cadbury No. 1, was transported to the GWR.  The steel two-road locomotive shed (known by volunteer staff as 'the Dowty shed') was also moved and it continues to stand at Toddington to this day.

Dowty Railway Preservation Society started concentrating on laying the narrow gauge railway at Toddington and changed its name to the North Gloucestershire Railway Company.  However, Cadbury No. 1 enjoyed its moment of glory when it operated the first public train on 22 April 1984.  This was a 'push-pull' service, and all trains on the GWR were so operated until the line reached Winchcombe in 1987 where a run-round loop was installed.

The little Avonside tank remained the only steam locomotive available at the GWR until the end of 1985 when its 10-year boiler certificate expired after a year-long extension and Peckett 0-4-0ST John took over (this locomotive remains at Toddington and is awaiting overhaul). However, as the line grew, small industrial locomotives were clearly becoming less appropriate and the North Gloucestershire Railway Company decided to sell engine to the Birmingham Railway Museum at Tyseley. It was overhauled and spent a number of years operating there before, once again, its boiler certificate expired and it has since remained stored next to the Tyseley turntable.

Now, Cadbury No. 1 is about to have another short spell in the public eye. To mark the 25th year of operation on the GWR, it is to appear at the 25th Anniversary Cotswold Festival of Steam, 23rd to 26th May 2009.  Although not in steam, it is receiving a cosmetic overhaul and appears resplendent in its smart Cadbury livery - complete with gold leaf graphics on the tank sides.

It will be a reminder of how far the GWR has gone over the past quarter of a century.  From 0-4-0 tank locomotive to the might of a British Railways 9F 2-10-0, the railway's motive power is a powerful reminder of just how much the railway has progressed.

What will the next 25 years bring as the little acorn continues its growth into a mighty oak?

• For key dates in the GWR's history, visit the chronology
• There is an excellent summary of the early history of the Gloucestershire Warwickshire Railway on the Railway Archiving Trust's website