Top judges today refused to pass a potentially lifelong sentence on a Corsham sex predator who kept a diary detailing his repeated abuse of a vulnerable schoolgirl.

Daryl Patrick Daffin, 48, was jailed for five and a half years at Salisbury Crown Court in September after admitting 22 counts of sexual assault, assault by penetration and taking and possessing indecent photos of children.

But his case reached London's Appeal Court today as lawyers for the Solicitor-General, Edward Garnier QC, urged judges the sentence was "unduly lenient" and that Daffin was so dangerous he should be locked up indefinitely for public protection.

The scale and impact of his crimes deserved an open-ended sentence,almost identical to a life term, from which he would only be freed once the authorities were convinced he was safe to return to the community, it was argued.

Lady Justice Rafferty said Daffin carried out repeated acts of sexual abuse, preying on his victim who he callously stripped, groped and fondled.

Daffin, of Sandy Lea Avenue, Rudloe, even filmed himself as he violated the youngster, the court heard, and kept a diary in which he detailed his exploits.

On top of that, Daffin also amassed a vast hoard of child porn from the internet, the court heard, totalling around 30,000 images of varying degrees of depravity.

Lawyers for Mr Garnier noted the "sophisticated grooming" behind Daffin's attacks on his victim, but conceded there was now evidence of remorse.

The judge, sitting with Mr Justice Globe and Mr Justice Leggatt, accepted the extreme gravity of Daffin's crimes and their "significant impact" on his victim.

But his offences did not justify an indefinite jail term, she ruled, refusing to increase Daffin's sentence.

Although some might "argue with force" that Daffin's punishment "tended towards the lenient", she said she was "not persuaded that the sentence was unduly lenient".