Tony Beeton was head of the Rights and Equality Division at Stormont and a close aide of Secretary of State Mo Mowlam.

An NIO spokesman said: "His work was respected by colleagues and ministers. The Secretary of State shares the deep sadness of all who have heard the new and has sent a personal message to the family."

Mr Beeton, an equality and human rights expert, is thought to have been killed while travelling to London from his home.

He was instrumental in drafting legislation for the new Human Rights and Equality commissions which have just been established in Northern Ireland.

Mr Beeton held several important roles in the Northern Ireland Office during his career.

He was the principle person involved in setting up the Bloody Sunday Inquiry after it was announced by the prime minister.

When talks with Sinn Fein began in public in the 1990's, he was a key contact with the party.

Downing Street said Tony Blair had been shocked to learn of Mr Beeton's death.

A spokeswoman for Mr Blair said: "The Prime Minister and Mo Mowlam are both shocked and saddened by news of his death, and have sent condolences to his family."

The spokeswoman added: "Before he joined the Northern Ireland Office, he (Mr Beeton) was involved in the Labour Party, from where the Prime Minister knew him.

"It is only in the last few hours that we have heard that he was one of the victims."

Mr Beeton, from Didcot, is survived by his wife and two children. He was based mostly in London.

Relatives visit crash site

Relatives of those thought to have perished in the London rail crash have visited the site.

The BBC's Graham Satchell: "For the relatives the visit will be the start of the grieving process"

Police said a total of 127 people were still missing following Tuesday's head-on crash between two trains, although only 30 bodies have so far been discovered.

About 45 relatives, and several injured survivors, were taken to the crash scene at Ladbroke Grove, not far from Paddington station, on Thursday afternoon.

The group, accompanied by counsellors and clergymen, were escorted to the trackside by British Transport Police officers.

Many carried flowers. One woman wept as she was brought closer to the wreckage.

Superintendent Tony Thompson, of British Transport Police, said: "This will obviously be a very distressing time for them but some relatives feel that it is a necessary part of the grieving process.

"They are convinced that their loved ones have died."

Police say they have managed to whittle down the number of people missing after Tuesday's crash, but the toll could still move past 100.

Of the 30 people still in hospital, four remain critically injured.