Ending Western tariffs would be the most fitting memorial to those killed in the Asian tsunami disaster, Tory leader Michael Howard has said.
The British public gave a lead on the aid appeal, say the Tories
Mr Howard said it was "immoral" for developed countries to perpetuate poverty through protectionism.
He was responding to a Commons statement by Tony Blair, who said UK direct aid was increasing to £75m.
Lib Dem leader Charles Kennedy said the crisis should enhance, not deflect, efforts to help Africa this year.
The confirmed tsunami death toll has now topped 150,000, including 51 Britons.
Two weeks on from the disaster, Mr Howard said it was still difficult to comprehend its "awful and awesome" scale.
He said the European Union and US had imposed tariffs on clothes from Sri Lanka, and Thailand had faced new tariffs since the tsunami struck.
He asked whether the prime minister had spoken to the EU Trade Commissioner, Peter Mandelson, about the issue.
Mr Howard continued: "Protectionism by developed countries at the expense of the developing world must come to an end. It is both indefensible and immoral.
"Would ending it not be the most fitting tribute to the generosity of the British people and the most fitting memorial to those who have so tragically lost their lives?"
Mr Howard said it was the British public, not politicians, who had given a lead in the generous response to disaster appeals.
He urged the government to extend Gift Aid - which allows charities to claim back tax funds - to collection boxes and to telephone donations without red tape.
There should also be a United Nations audit to ensure all countries delivered on all their aid pledges, he said.
For the Lib Dems, Mr Kennedy also said it was important governments were held to account over their aid promises - which had failed to materialise in other crises.
With the UK chairing the G8 group of industrialised nations this year, Mr Kennedy said its hopes for helping Africa should not be diverted but enhanced by the new challenges.
Mr Kennedy paid tribute to UK officials who had helped families with missing relatives.
And he suggested the UN could set up a permanent rapid reaction force to help cope with future crises.
He added: "It has been a most hellish and most unimaginably grief stricken period...
"But what we can contribute as a House of Commons constructively with impractical measures will go some way to giving people a sense that their politicians are responding to the most fundamental human needs of all."
Mr Blair said it was important to track the delivery of the aid money, although he thought it would be produced this time.
The Inland Revenue was also looking at the Gift Aid issue, he said.
And on Africa, the prime minister argued aid and trade were important but conflict resolution and governance had also to be addressed as part of a comprehensive package.