An art teacher was warned that he was facing jail yesterday after admitting a long-running affair with a 15-year-old girl.

The pupil told police that Ian Blott, 54, groped her in cupboards and sent her text messages saying "I love you" and "You are beautiful".

They formed a relationship after having sex at a hotel in Edinburgh, where the class had gone to study art, and on a trip to France, the girl said.

She told Hull Crown Court that Blott, married with two children, also sent her explicit photographs of himself from his camera phone.

Helen Hendry, prosecuting, said: "They had a two-and-a-half-year relationship of some intensity with sexual activity and sex taking place outside school and on school trips."

Blott, of Thwing, East Yorkshire, a teacher for 30 years, pleaded guilty to two specimen charges of abusing a position of trust and two of sexual activity with a child.

He denied that sex took place on school trips or on school premises but admitted the affair and on occasions having full sex.

Miss Hendry told the court that there was no public benefit of Blott going on trial to determine the extent of sexual activity because it would mean the girl being put through the ordeal of giving evidence.

Blott became the subject of a police investigation after the girl confessed to her mother, who told the head teacher.

He told detectives that he had thought the relationship was legal as the girl was by then 16. He did not realise that the Sexual Offences Act 2000 and 2003 had outlawed teacher-pupil affairs.

Judge John Dowse ordered background reports before sentencing. He told Blott: "Your plea means that you must expect to go to prison for some time. I understand that [the girl] has been very considerably affected."