A former Sussex head teacher has escaped jail for indecently assaulting pupils after Crown prosecutors failed to have his sentence increased.

Robin Peverett OBE - the former head of the Countess of Wessex's prep school - pleaded guilty last June to nine counts of indecently assaulting pupils.

Peverett, 67, of Battle, near Hastings, was given an 18-month suspended sentence.

The Court of Appeal today blocked a bid by the Attorney General to have him imprisoned on the basis his sentence was unduly lenient.

Three appeal judges held that the sentence on Peverett, former head of Dulwich Preparatory School in Cranbrook, Kent, could not now be challenged because the prosecution was actively involved in "plea bargaining" which led to his pleading guilty on the promise he would not go to jail.

Last June at Maidstone Crown Court Peverett admitted nine counts of indecently assaulting pupils between 1969 and 1977.

The assaults were on six girls and one boy, aged between ten and 13.

Most of the offences involved tapping or fondling the children's bare bottoms as punishment, sometimes in the school oast house where he lived and where he would give individual tuition.

Peverett, who had initially denied indecent assault, pleaded guilty on the basis that seven other charges would not be proceeded with, that he had received no sexual thrill from disciplining and exercising power over the children - and that he would not go to prison.

Today, Lord Justice Rose, sitting with Mr Justice Astill and Mr Justice Richards, said the "lamentable history" of the case demonstrated the wisdom of earlier decisions of the higher courts which for years had "set their face against plea bargaining".

He said: "The public are likely to be affronted by that sort of process."

One victim was close to tears after the appeal hearing.

The Crawley woman said: "I'm devastated, absolutely devastated.

"We fought so hard and a decision made behind closed doors without reference to the victims at all has left us with no justice."

The mother of three said she was the subject of Peverett's attentions for 18 months between the ages of 10 and 12.

She said: "He used us as children. He put us through nearly a quarter of a century of hell."

She added: "I've got on with my life but it's always in there in my head."

Peverett was head of the £7,000-a-year private school when Sophie Rhys-Jones was a pupil between 1969 and 1976. She knew nothing of the offences.

The crown court heard that an 11-year-old girl being taught Latin would get sweets for a correct answer and a smack for a wrong one.

Peverett got her to gamble either one, two or three sweets on the answer, corresponding to a smack with clothes on or with knickers on or on the bare bottom for a wrong reply.

The offences came to light after one victim spotted Peverett on television during coverage of Sophie's engagement to Prince Edward.

The victim spoke to her husband about what had happened all those years ago and he urged her to go to the police. Others followed suit.

Peverett was awarded the OBE in 1995 for his work in education. He was an adviser to the Thatcher government and a chairman of the Independent Association of Preparatory Schools.