Andrew Hunter, chairman of the Tory backbench Northern Ireland committee, said: "On the assumption that this is another IRA bomb then our worst fears are fulfilled.
"It is another horrific outrage. It is sickening and there is no justification. The IRA will win no concessions by this course of action."
Ken Maginnis, security spokesman for the Ulster Unionists, also immediately identified the bomb as the work of the IRA. He said: "Until we face up to the reality of what the IRA really are we are going to suffer this type of tragedy again and again.
"From much of the media reaction to the Canary Wharf blast one would have thought that the Unionists had brought the bomb across into Great Britain and John Major had personally planted it.
The Rev Ian Paisley of the Democratic Unionist Party said: "This is a funny way to put out the hand of friendship by murdering people.
"You can't negotiate with people who who are prepared to take up weapons and take lives."
Peter Robinson, DUP MP for East Belfast, said: "I think that the time has come that the whole international community must be prepared to crush the Provisional IRA."
The Ulster Unionist MP John Taylor told BBC Radio Five Live: "If people are letting off bombs in buses as the IRA have apparently done tonight, then the peace process is over in the meantime.
"We have to concentrate on saving people's lives."
The former Northern Ireland minister Peter Bottomley said that the IRA feared democracy. "In elections for the all- party talks, they must have expected to receive less than their past share of the vote in Northern Ireland.
"That is the only rational explanation for the Sinn Fein/IRA return to violence."
The bomb occurred on the eve of today's Commons debate on the Northern Ireland Emergency Provisions Bill.
The Tory MP David Wilshire, vice-chairman of his party's backbench Northern Ireland Committee, said: "On the assumption it is another IRA bomb, we have definite proof now of an ongoing campaign.
"The IRA has come to the conclusion that it is not going to get a united Ireland through talks and will only do so through bombing the English into submission.
Gary McMichael, leader of the fringe loyalist Ulster Democratic Party, expressed concern about the "prospect of a full scale resumption of violence."Reuse content