By Glen Owen and Richard Creasy

Last updated at 21:02 14 October 2006

A female teacher at one of Britain's most prestigious public schools has been disciplined after being caught in a "compromising situation" with one of her sixth-form pupils.

Lucia Quinault, the head of English at Winchester College, who is in her late 30s, was found with an 18-year-old boy after a celebratory dinner at the school.

Mrs Quinault, who is married to a senior civil servant in Whitehall and has three children, received a "severe warning" but kept her job.

It is the latest in a string of troubles at the 600-year-old school, including the 2003 arrest of an ex-housemaster over sex abuse allegations, which were later dropped.

According to a school insider, the incident happened after a leavers' supper at a school boarding house with the nickname Hopper's.

"A tutor spotted her embracing the boy in the street,' the insider said. "The boy was one of her pupils, with known literary interests, and had associated closely with her over the previous year.

"Another don also saw them together, a little further away."

The first tutor reported what he had seen and, after the boy had been missing for three hours, his housemaster sent out a search party. They found him at Mrs Quinault's home.

Winchester headmaster Ralph Townsend interviewed the teacher and the case was investigated by the school's child protection officer.

"She claimed that she had been comforting the boy after he had broken up with his girlfriend,' the source said.

"She was given a severe warning but allowed to keep her job."

Her husband, James, Director of Managed Migration at the Home Office, was this year caught up in a row over the number of asylum seekers at large after admitting National Insurance numbers were given out 'like Smarties'.

Last night, the school said: "The matter was investigated thoroughly at the time. It was dealt with promptly and properly and there is nothing further to add."

When approached by The Mail on Sunday at the home he shares with his wife in the Hampshire town, Mr Quinault shouted '**** off' and slammed the door.

The incident is the latest problem at the £25,000-a-year school - motto Manners Makyth Man - which regularly tops league tables.

Three years ago, the school's head, Nick Tate, resigned after complaining of a campaign of vilification against him by the school's "dons".

In the same year, the school was caught up in allegations of fee-fixing with other schools.

It was later found guilty of anti-competitive practices by the Office of Fair Trading.