The Palestinians' push for recognition of independence at the United Nations later this month was criticised as counterproductive to the chances of peace at a packed Westminster meeting on Monday night.
Former Spanish Prime Minister José Maria Aznar, who is founding chairman of the Friends of Israel, said that if the UN General Assembly backed the Palestinians' declaration of statehood, "it would push away any prospect of any final peace agreement".
Mr Aznar said that governments should insist that the only way to end the Israeli-Palestinian conflict was around the negotiating table.
"It is time to tell the Palestinians if they really want a state, they must pay the price for it," he said. "They cannot have the cake and eat it."
The UN initiative would "serve only to delegitimise even more the state of Israel" and "encourage and nurture a new offensive campaign of lawfare against Israel", he warned.
Elliott Abrams, a former American deputy national security adviser, said that American politicians were united against the Palestinian recognition bid. "Everyone agrees that this Palestinian move will set back the cause of peace," he said. "It will become an obstacle to moving forward toward any kind of improved relationship between Israelis and Palestinians."
Mr Abrams, now based at the Washington think tank, the Council of Foreign Relations, also spoke at an all-day conference on the potential fallout from the UN vote at the Royal United Services Institute (RUSI) in London.
Nabil Sha'ath, the Palestinians' chief negotiator with the Israelis in the 1990s, told RUSI that the UN move was not a substitute for peace talks.
He declared: "This declaration of independence is morally, politically, legally, diplomatically - and in every other way - a legitimate non-violent way for the Palestinians to try to get the Israelis back to real negotiations."
● Meanwhile, the Board of Deputies and the Jewish Human Rights Coalition UK have written to Foreign Secretary William Hague, calling for Britain to withdraw from the "Durban III" human rights conference at the UN.
Board president Vivian Wineman and JHRC chairman Rosalind Preston wrote: "This meeting is an ill-judged attempt to 'celebrate' 10 years of a process that has been acknowledged to have been deeply flawed from its inception and to have become synonymous with displays of intolerance and antisemitism."