A teacher who committed sex offences as a teenager almost half a century ago has been jailed by leading judges who overturned his "unduly lenient" suspended sentence.

Lord Chief Justice Lord Thomas and two other Court of Appeal judges in London imposed a prison term of three and a half years in the case of Gordon Gamble, 64, of Filching Road, Eastbourne.

They agreed with Solicitor General Robert Buckland that Gamble - described as an "exemplary teacher of distinction" - should have been been jailed immediately when he was sentenced at London's Snaresbrook Crown Court in November.

Gamble, who was found guilty of acts of gross indecency with a child, committed offences between March 1967 and March 1970, beginning when he was 15 and his victim was nine.

Lord Thomas stressed that when judges sentence in cases involving "historic offences" they must "guard against any temptation that because of what has happened in the intervening years one arrives at a decision where a sentence can be suspended".

The judge who imposed a two-year suspended term had referred to a number of matters, said Lord Thomas, including the fact that the offences "had been committed almost 50 years ago when the offender was a teenager", that he was acquitted of seven of the original 10 counts, had no previous convictions and had worked as a teacher.

Lord Thomas said it was "important to appreciate that the counts were specimen counts".

Referring to the victim, he said: "She has lived with this matter for close on half a century. It has clearly had a most devastating effect on her life."

The "appropriate sentence" which should have been imposed was four years imprisonment.

Lord Thomas said the court considered an allowance could be made because Gamble had already completed 40 hours of an order to undertake 300 hours of unpaid work - resulting in a sentence of three and a half years.

Mr Buckland said in a statement after the hearing: "I decided to refer this matter to the Court of Appeal because I felt that the sentence did not reflect the prolonged pattern of offending and the impact on the victim.

"These offences did not come to light for nearly 50 years. Prolonged sexual abuse has a terrible impact on its victims. I am glad therefore that the Court of Appeal has seen fit to increase the sentence in this case."