Is it Wills or not?

Is it or isn't it? Even his own father would have trouble recognising the young man caught laughing hilariously beneath a mountain of shaving foam.

The question now being asked of this picture, taken during student celebrations at St Andrews University's Raisin Monday, is whether it shows Prince William.

The Mirror newspaper insists it does. Buckingham Palace is not so sure. "We don't think it is him," one royal press officer told the Evening Standard.

Doubts have been raised by the telltale gap in the young man's teeth. Other pictures of Prince William, including the portrait used on this page, show no such dental flaw.

Meanwhile, the Times's Scotland correspondent, Gillian Harris, stated categorically today that William had chosen to stay away from the event.

But the Mirror was today sticking by its story. Insiders at the paper said they had been told by reliable sources that William attended the foam fight. "We are satisfied it is him," said one.

According to the tabloid, the 19-year-old joined a thousand fellow students in the giant foam fight. First, it said, he painted his hair blue, then he threw himself into the fray.

It is understood Prince Charles had warned William to stay away from the traditional week of celebrations but, if the paper is to be believed, the fun-loving prince appears to have ignored his father's advice.

Raisin Monday has a reputation as the Scottish university's most uninhibited party of the year. The tradition dates back to the 15th century and sees first-year students in fancy dress engage in various high jinx in the ancient St Salvator's Quad.

The Mirror quoted an insider as saying: "He was keen to take part even though many people thought he wouldn't because of the potential embarrassment. Wills didn't want to be seen as prude. He has always said he wants to be treated just like any other student."

His fellow students wore a range of outfits, from a giant Guinness can to a Marge Simpson costume. Some of the girls seemed to wear rather less, but there was plenty of foam on hand to spare any putative royal blushes. According to the Mirror two undercover police officers were never far from the Prince's side.

Understandably many of the students had little idea the Prince was supposedly among them.

Italian biology student Linda Sebastianutto, 23, who was dressed as a bee, said: "This has been a fantastic experience. There was a rumour that Wills was here but as far as I know I haven't seen him. I probably wouldn't have recognised him anyway - everyone is covered from head to toe in foam."

The quadrangle lawn, the size of three tennis courts and a matter of yards from Wills's front door, was quickly covered in foam, as were many of the ancient buildings.

Some students had come wrapped in clingfilm but to no avail. By the end everyone was indistinguishable from everyone else - even from someone as famous as William.