A prison officer has resigned following claims she had an "inappropriate relationship" with a murderer who strangled his former girlfriend with his belt, it was revealed today.

Shirley Fowle, 42, fell for 28-year-old Alan Dalby while serving his sentence at HMP Swaleside on the Isle of Sheppey, Kent, the Sun newspaper reported.

A Prison Service spokesman said today: "A prison officer resigned last week from HMP Swaleside following allegations of an inappropriate relationship with a prisoner."

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Ms Fowle told the Sun: "Everybody has a past - everybody tries to kill someone in their temper. I haven't had sex with the guy. All I did was have a relationship."

Dalby was convicted at Maidstone Crown Court in October 2002 of murdering student Natalie Janiak, 18, either in his home or in the back of a friend's van after having consensual sex with her.

He tried to cover his tracks by telling mutual friends, her mother and the police that he and Natalie had gone to a common in Blackheath, south-east London, for sex.

Dalby claimed that they had argued and that Natalie stormed off, never to be seen again.

But he confided to a female friend that he had killed Natalie, and, despite covering for him at first, she later told police about his confession.

To start with, Dalby maintained his original story that he and Natalie had rowed before she vanished, but shortly before his trial he admitted he had killed her.

He then concocted a further story, claiming he restrained Natalie with a belt after she went berserk when the friend told her she was pregnant with Dalby's child.

A judge said the accounts Dalby gave for Natalie's death were "all implausible" and that it was impossible to know his true motive for murdering her.

Speaking following Ms Fowle's resignation, the Prison Service spokesman added: "The vast majority of our staff are honest and hard working, but one corrupt officer can jeopardise the safety of the whole prison.

"Swaleside Prison supports a culture which values integrity above all and rejects corruption and dishonesty wherever it is found."

HMP Swaleside is a Category B prison for inmates serving four years or more or should have at least 18 months left to serve.

It has 460 places for lifers and has an operational capacity of 954.