Prime Minister Tony Blair vainly tried to change the subject from his political fate Wednesday as the leader of the British opposition urged him to "go, and go soon."

Conservative leader David Cameron, whose party was energized by thrashing the governing Labour Party in local elections last week, pressed Blair aggressively in Parliament, saying "the prime minister won't even address the fact that he's losing the support of his party."

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Labour's poor election showing followed a string of troubles for the government, including big financial problems in the National Health Service and officials' acknowledgment that more than 1,000 foreign criminals were released without being screened for deportation.

Deputy Prime Minister John Prescott caused further embarrassment by acknowledging just before the vote that he'd had an affair with his secretary. She claimed in a newspaper report that the two had sex in Prescott's government office, prompting a complaint that he should be investigated for misconduct.

Police said Wednesday they would not investigate. Metropolitan Police Deputy Assistant Commissioner John Yates said the allegation, even if proved, was not serious enough to warrant prosecution.

"Aren't the crises in the health service and the criminal justice system symptoms of a government that is paralyzed?" Cameron demanded in Parliament. "Isn't it becoming increasingly clear that he should go, and go soon?"

"Let me thank you for that very kind advice," Blair retorted sarcastically.

The prime minister said he wanted to talk about policy matters and accused Cameron of having little of substance to say.

"I've got no interest in debating that with him," he said in response to another Cameron question about his plans. "Again I simply issue the invitation to debate policy."

Blair has said he plans to serve a full third term, but this week reassured Labour lawmakers that he would step aside in time for his successor to settle into office before the next general election, expected in 2009.

The worries among Labour lawmakers are unlikely to die down unless he gives in to pressure to make a private deal with his likely successor, Treasury chief Gordon Brown, about the timing of an eventual handover, said Phil Cowley, a University of Nottingham politics expert.