As robust as the monarch after whom she is named, the gleaming maroon Pacific Princess Elizabeth is steaming on into a venerable old age. The 79-year-old locomotive has been a star of the rails since the day of her construction, to the design of the London, Midland & Scottish Railways’ chief mechanical engineer Sir William Stanier. (whose nephew Robert was later to become Master of Magdalen College School, Oxford).

Her most celebrated early exploit took place three years into her career when she was responsible, travelling between London and Glasgow, for the fastest and longest non-stop steam-hauled run in the record books. On June 3 this year, she achieved worldwide stardom when her whistle, heard from Battersea Railway Bridge, signalled the start of the Thames Diamond Jubilee Pageant. On July 11, Queen Elizabeth travelled behind ‘her’ engine for the first time as part of her Diamond Jubilee Tour. One leg of the trip brought the engine from Worcester to Oxford.

Princess Elizabeth’s recent celebrity made her the ideal substitute — almost the only acceptable one for me — when Steam Dreams was obliged to find a replacement last week for the indisposed Standard Pacific Britannia on a Cathedrals Express trip from London to Chester. Like many people from Oxford, I had booked seats on the excursion. No. 70000 Britannia was built in the year of my birth, 1951, and the outing was intended to make up for my disappointment over the cancellation of a trip with her earlier in the year owing to a union dispute. Oh well, another time . . .

With Princess Elizabeth, the next time might have to wait a while. Last Tuesday’s excursion, on which she performed magnificently, was her final duty before being taken out of service for the major overhaul preserved steam locomotives must receive every ten years, whether or not there is anything obviously wrong with them.

As the Steam Dreams onboard commentator explained: “They have to be taken apart in order for engineers to discover that there is nothing to repair.”

The engine’s appointment at Tyseley Locomotive Works, in Birmingham, meant she was unable to haul the 11-coach train on its return from Chester. The job was done — with soulless efficiency — by a class 67 diesel electric.

Mention of Tyseley reminds me that this former engine shed (code 2A) was one of the many I ‘bunked’ (visited without permission and with a wary eye for the foreman) during the dying days of steam. I retain a vivid mental picture of the woebegon parade of grimy Great Western ‘Granges’, ‘Halls’ and ‘Castles’. ‘Counties’, too — the pioneer member of the class, No. 1000 County of Middlesex was among their number. None of these handsome two-cylinder locomotives survived into preservation, though construction of a replica, to be called No. 1014 County of Glamorgan, is under way at the Great Western Society’s headquarters at Didcot.

Having referred to the Great Western, and writing as I am for a readership firmly in that company’s former territory, I feel compelled to point out the GWR’s link with Princess Elizabeth. Sir William Stanier was ‘poached’ by the LMS from the GWR and took with him a great deal of its expertise. The ‘Lizzies’, as they were affectionately known, were basically ‘Kings’ with the addition of a pair of trailing wheels.

There were 13 of the class in total — for once this proved a very lucky number.