Charities have criticised what they call the “lenient” prison sentence given yesterday to a teacher who had a gay relationship with a pupil.

David Le Brocq, 30, is expected to only serve part of his one year sentence.

He was found guilty of conducting a six-month sexual relationship with Karl Donaldson, then aged 15.

The court heard that the pair had “full sex” in Le Brocq’s flat when when the boy was 16 with approval of Mr Donaldson’s mother, Donna Stacey.

Michele Elliott, the director of the children’s charity Kidscape, said: “It does not matter if it was consensual: the point is that when you are a teacher you are in a position of authority over a pupil and you do not have sexual relationships with them. “Given that he could be out in six months it seems to me that he has got off very lightly.”

Mr Donaldson, who waved the right to anonymity, told the Reading Evening Pos: “I have not been in touch with him since we broke up and just want to forget about what happened and get on with the next chapter in my life.”

The relationship ended in August 2004 when Le Brocq said he was going to have a child with a colleague.

When he was arrested in September 2005, Le Brocq was deputy-head teacher at Bovington Middle School in Wareham, Dorset.

Alan Blake, for the prosecution, told the court: “He loved David Le Brocq and his mother wanted him to be happy. The evidence is that there was a mutual infatuation between them.

“David Le Brocq exercised some restraint in not allowing matters to progress too far physically before the boy’s 16th birthday.”

Judge Anthony King said yesterday: “It is perfectly apparent that the boy was already a person who was attracted to you. Indeed, much that occurred was at his instigation. Sadly, though, this case is a classic example of a substantial and serious breach of trust.”