Staff at University College Hospital said Mr Heffer, a nurse aged 30, was not able to breathe without assistance and they believed his brain was so extensively damaged he would never recover. Mr Heffer's mother, father, sister and girlfriend were at his bedside.
Mr Heffer was very near the device and took the full impact of the explosion at lunchtime on Monday. The IRA admitted planting the device - the eighth explosion in London in six days.
The IRA yesterday denied that it was involved in an incident at Dungannon, Co Tyrone, in which a suspected assassination squad was disturbed while trying to infiltrate a council meeting. There was speculation that Ken Maginnis, a local councillor and the Unionist MP for Fermanagh-South Tyrone, was the target for the two-man team which fled when challenged, but Sinn Fein sources said they believed that the men were loyalists attempting to kill nationalists.