An informer who infiltrated the IRA for the British intelligence agency MI5 has been found dead in his flat in England, according to reports. 

Raymond Gilmour, 55, was a "supergrass" witness in a 1984 case in which more than 30 members of the Irish Republican Army (IRA) paramilitary group were arrested in his native Derry, in Northern Ireland.

The 55-year-old's badly decomposed body was found at his home up to a week after he apparently died of natural causes, according to the Belfast Telegraph.

The 1984 case collapsed and Mr Gilmour was resettled in England and given a new identity. But he broke cover in 2012 to complain that he had been abandoned by his security services handlers.

He told BBC television they had promised him a financial sum, a new home, a pension and psychiatric support, but said he only received modest accommodation and a small monthly allowance for three years.

Mr Gilmour's friend and fellow agent, Martin McGartland, told the Belfast Telegraph: "It is disgraceful that Ray died in these circumstances.

"He spent years begging MI5 for financial and psychological help. Instead, they turned their back on him.

"He was a broken man, a wreck of a human being, and they left him to die in the gutter."

The newspaper reported that Mr Gilmour was found in his flat in Kent, southeast England, by his 18-year-old son.

The funeral will take place next week.

Kent police did not immediately respond to a request for comment.

The IRA waged a violent struggle to end British control of Northern Ireland that endured for three decades before the 1998 Good Friday Agreement largely brought peace to the province.