There are chandeliers in the gym, a labyrinth of secret tunnels built by an eccentric duke beneath the grounds and the Crown jewels were stashed there after the First World War.

But now Welbeck college in Worksop, Nottinghamshire - the country’s only sixth-form training college for officers in the Army’s technical corps - is breaking with its long tradition and moving to a new multi-million pound site down the road in September 2005.

With pound;300 million from a Private Finance Initiative deal, the education consortium Minerva will build a training centre which will also serve the Navy, the Air Force and the civil service. Pupil numbers will increase from 225 to 375, and staff from 24 to 34.

Tony Halliwell, 49, Welbeck’s headteacher, said: “Some Navy and Air Force students will start in September. The changeover is going to be a big challenge.

“The students are quite conservative in their views. They want to keep the Welbeck logo and the uniform, which is an old-fashioned tweed jacket. We have had it for years and they are devoted to it.”

The new 45-acre site in Woodhouse, Loughborough will have an indoor swimming pool, a floodlit synthetic football pitch as well as four rugby, four soccer and four hockey pitches - twice as many as at present.

The old school’s buildings, which belong to the Duke of Portland’s family and are leased to the Ministry of Defence, are difficult to adapt because they are grade I and II listed.

Mr Halliwell said: “Our gym is a sunken ballroom with 17 chandeliers in it, so we can’t play ball games. We store canoes in one of the tunnels that the Duke of Portland built, and one of the rooms in my house was where the Crown jewels were stored for safe keeping in 1918.

“We are trying to operate a modern sixth-form technical college. But because of certain English Heritage restrictions, we do not have an indoor swimming pool or a floodlit synthetic pitch. Half of my operational costs go into maintaining the buildings. We have to move on.”

Every summer, the lower sixth-formers take part in a military training camp near Helensburgh, Scotland, where they have to storm a house and capture “insurgents” played by former Welbeck students who are at university.

Pupils use standard Army-issue rifles loaded with blanks.

“Sometimes they get overexcited and point a rifle at someone’s head,” said Mr Halliwell. “If they do that, I have to grab the butt and point it at the ceiling.”

A spokeswoman for the Ministry of Defence said: “All three armed forces and the MoD need more engineers and technical specialists and scientists, and this college will address that need.”