A showman's locomotive built in Thetford in 1907 is expected to fetch up to �650,000 when it is auctioned on Saturday.

The travelling fairgrounds of a century ago provided a moveable palace of engineering wonders – with this crimson loco crowned as its royalty.

And although the showman's heyday of carousels, gallopers and pipe organs may be long gone, His Majesty's regal reputation has continued to grow.

So much so, that this Norfolk-built king of the entertainment world is expected to bring a princely sum of up to �650,000 when it is auctioned on Saturday.

His Majesty, also known as Burrell Road Locomotive No. 2877, left the Thetford factory of famed steam engine builder Charles Burrell in 1907.

It spent its entire working life with leading Somerset showmen and roundabout proprietors Charles Heal and Son, of Somerset, who used it to transport and power their rides at fairs and carnivals until the 1940s.

Auctioneers hope those historic connections with both East Anglia and the West Country will force some competition between deep-pocketed bidders when the engine goes under the hammer in Cambridgeshire.

Bill King, a director of specialist firm Cheffins, said His Majesty's value was duue to its rarity, its unique provenance and the nostalgia it would generate among steam enthusiasts.

'It is very evocative of the era it represents,' he said. 'Engines like this are very, very rare coming onto the auction market and people who aspire to owning one may only get one chance.

'We are hoping we have got our valuation right and we are hoping that we get more than one buyer interested. I suppose the big driving force behind the buyers is a desire to preserve our heritage. But a limiting factor is that they need to be someone who has substantial funds behind them.

'Heals owned this particular engine from new until 1959 so it has got fantastic showman's history and provenance.

'But it has history in Norfolk too. Burrell was the main maker of showman's locomotives. With the reputation he had, he cornered the market in these engines. 'They were the ones everyone wanted in 1907, and they still are.'

By the end of the 19th century, steam-driven locomotives had become the workhorses of Britain's agricultural economy.

Meanwhile, fairground rides and attractions developed from small, hand turned rides on village greens into large, complex machines requiring major sources of power.

Showman's locomotives like His Majesty were developed to drive this new generation of entertainment.

'They were dual purpose, as not only would they pull the rides, but they had a dynamo mounted at the front which would generate the electricity to run them,' said Mr King. 'It was what every showman wanted and needed to run their business.'

His Majesty was used by the Heal family throughout this period to power rides which fired the imagination of children across the country – galloping horses, dodgems, a Noah's Ark, a skid and a moon rocket.

Since 1959, the engine has been restored to its gleaming best by a succession of owners including Norfolk enthusiasts Ben Brock and Arthur Mason. It is being sold following the death of its most recent owner, Devon collector John Lee.

?The locomotive, with an estimated price of �550,000-�650,000, will be sold at Cheffins' Vintage Sale on Saturday, July 23, at the company's saleground at Sutton, near Ely.