From this article, Vietnamese shouldn't thank Thatcher, which deals with boat people entering Britain from Vietnam in 1979 and what he claims was misplaced gratitude to Margaret Thatcher by Mark Tran, we learn of Menachem Begin's influence in matters of humanism:
...newly-released Downing Street papers...released by the National Archives, showed that [Prime Minister Margeret Thatcher] only very reluctantly agreed to take the Vietnamese refugees and only did so after much arm-twisting by Lord Carrington, then foreign secretary, and William Whitelaw, then home secretary. These are the real heroes behind the decision by Britain to accept 10,000 Vietnamese refugees.
...Despite his reputation as a wet, Whitelaw took a strong stand. "It is necessary that we should have a positive and defensible policy towards refugees from a brutal communist tyranny," the home secretary said. As for Carrington, he pointed out that Britain would look pretty bad if it did not come up with a signficant offer especially as the UN conference was Thatcher's idea to start with. Thatcher also came under strong international pressure. Menachem Begin, the Israeli prime minister, had written to Thatcher in June 1979 criticising her idea of a conference and suggested that each country accept a certain number of refugees as a way of dealing with "this horrific tragedy".
Eventually Thatcher relented and decided that yes, Britain would take 10,000 Vietnamese refugees.