Controversial judge Julian Hall today let a teacher who had sex with a 15-year-old boy walk free after saying he wasn’t sure she harmed him.

Catherine Armstrong, 33, had promised the boy a “birthday bonk” for his 16th and had sex with him several times while he was still 15.

She initially denied the charges but then admitted two counts of sexual activity with a child and one of touching him while in a position of trust.

The teenager — who cannot be identified but has learning difficulties — asked Judge Hall at the trial to be “nice to her” when he sentenced her.

He said it took him “a stupidly long time to realise that what we were doing was wrong”.

Mother-of-two Armstrong, of Hunt Road, Thame, wrote emails to her young lover after the relationship broke down, in which she declared her love.

Yesterday Judge Hall — criticised in the past for his sentencings of paedophiles — gave Armstrong a 12-month prison sentence but suspended it for two years after calling the case unique. He said: “I find it impossible to decide if he has been harmed by what you did but you shouldn’t have done it.”

She will sign the Sex Offenders’ Register for five years.