So who is the ghost of Peterhouse?

A spectre is said to be stalking the ancient cloisters of Peterhouse College, Cambridge, and witnesses swear that they have not been at the pre-Christmas port. Kathy Marks listens to a modern ghost story and speculates on the identity of this restless soul.

As the fellows of Peterhouse convened for lunch yesterday in the college's oak-panelled combination room, their minds were not, for once, absorbed by lofty intellectual matters. Instead, the talk at high table was dominated by one subject: a ghostly apparition that has been seen by three people in the very room in which the dons were tucking into their noisettes of lamb, dauphinoise potatoes and blackcurrant cheesecake.

The first sighting, by two butlers last April, was greeted with scepticism by the college community. But last month no less eminent a figure than Andrew Murison, the senior bursar, reported that he, too, had witnessed a visitation. Now the dean, the Rev Graham Ward, is considering an exorcism.

Speculation about the spectre's identity has reached fever pitch at Peterhouse, Cambridge's oldest and most fiercely traditional college, and the inspiration for Tom Sharpe's novel Porterhouse Blue. The front-runner is Francis Dawes, a former bursar who hanged himself from a bellrope in 1789 after the election of a very unpopular master.

But with a history stretching back to the college's foundation in1284, there are plenty of candidates among former fellows and alumni. The ghost, say some, could be James Mason, staging a posthumous comeback after his glittering film career. Or Kingsley Amis, the late novelist, returned to gather material for a sequel to Lucky Jim. Or James Clarke Maxwell, the 19th-century physicist, eager to show off his electromagnetism equations to a modern audience.

If political demise released wandering spirits, the field would be even wider. Michael Portillo and Michael Howard were both students at Peterhouse in the Seventies, when the college was a hothouse of ultra right-wing ideas. Mr Portillo's mentor at Peterhouse, which admitted women only in 1985, was Maurice Cowling, the historian who was highly influential during the Thatcher years.

The dean's plan to hold a requiem Mass to exorcise the spirit, whoever he may be, is pooh-poohed by Mr Murison. "A load of old mumbo jumbo," he said. "Anyway, he's not causing anyone any harm. It's not as if women undergraduates are throwing themselves out of windows."

Mr Murison, formerly an agnostic about ghosts, entered the dimly lit combination room late one evening and became aware of "a presence" in one corner. "At first I thought it was Max Perutz, one of our Nobel Prize winners, because it was smallish, slightly built and balding," he said.

"It was wearing a wide collar, like a pilgrim, and seemed to be holding a large hat. I moved closer to get a better look. I wasn't frightened in the slightest; I was more concerned about frightening it away. It was very benign. After a few seconds, it quietly disappeared. The room was very cold, although a fire was still burning in the grate. It was quite an extraordinary experience. I didn't mention it to the other fellows for a while. I'm supposed to be a financial administrator, not some nutcase who goes around seeing ghosts."

It was in the same 600-year-old room that Matthew Speller and fellow butler, Paul Davies, had seen a "cigar-shaped, person-sized apparition" moving slowly towards a bay window, about a foot off the ground. "When we first told the fellows about it, they treated it as a bit of fun," Mr Speller said.

Graduates of Peterhouse, who include Peregrine Worsthorne, the former Sunday Telegraph editor, say it is a perfect setting for a haunting. "It's definitely got vibes," said one. The fellows, anxious to protect their reputation for intellectual rigour, are divided. Dr James Carleton Paget, a divinity don, said: "I can vouch for the good witness of the bursar. He is a hard-headed financier who is a creature of the Enlightenment rather than of the pulpit."

But Lord Dacre, the historian, and former master of the college, said: "I was aware of some poltergeists in human form, but I never heard of any less substantial apparitions. Some people, even fellows of Porterhouse, will believe anything."