Lord Owen's warning came as John Major won the cautious backing of Parliament for reinforcements after telling a sombre House of Commons that he would not enter a "blackmailing deal" with the Bosnian Serbs to secure the freedom of the 34 British hostages in return for a pledge not to resume air strikes.
Mr Major confirmed that the 5,000-strong 24 Air Mobile Brigade - equipped with helicopters, anti-tank weapons, artillery and air defence batteries - would depart for Bosnia and would be deployed as UN troops under General Rupert Smith in Sarajevo.
British officials said the return of the hostages and the recognition by Belgrade of Bosnia would almost certainly be needed before urgent preparations to deploy the Brigade stood any chance of being halted.
Reinforcing earlier indications that the new "military muscle" was intended to prevent further hostage-taking and stop attacks on British and other UN troops, Malcolm Rifkind, the Defence Secretary, said in the Commons last night: "Should the need arise, robust tactics will be deployed."
He acknowledged that continued protection of the three UN "safe havens" of Gorazde, Srebrenica and Zepa was under review, under the policy of "concentrating" forces. Mr Rifkind said: "We believe it is appropriate to look at them to see whether the policy is tenable ... We have come to no judgment."
Lord Owen made it clear in his first speech to the House of Lords that he supported the decision to "nearly triple" Britain's 3,400 troops in Bosnia.
The "only way forward" in Bosnia was for the UN to be given "every assistance" to sustain its impartial humanitarian mission, he said. But Lord Owen warned that without fixing "exact deadlines" it should be made clear that the commitment depended on political progress and added: "If there is no settlement by the autumn of this year, I fear the UN forces would be forced to leave."
The Commons heard Mr Major's warning that troops in Bosnia needed more protection. The Prime Minister challenged the more restive Tory MPs to accept that Britain had a strategic interest in preventing an "all- out Balkan war", adding: "The bloodshed and loss of life would be massive. Before we sent troops three years ago, Bosnia was on the brink of genocide ... Depart, and these dangers return."
The sharpest exchanges came when Teresa Gorman asked him whether it was not possible to secure the release of the hostages by promising there would be no further air strikes. Mr Major declared: "I am not entering into that sort of blackmailing deal."
Tony Blair said that if force was allowed to replace the rules of international law, the UN would slide into the "same abyss" as the League of Nations.Reuse content