The UK should abandon its commitment to raise overseas aid by another 37% to meet a United Nations target amid painful spending cuts elsewhere and fears over value for money, peers said.
Pumping scarce cash into hitting an "arbitrary" 2013 benchmark was the wrong priority, an eminent committee warned - attacking Government plans to enshrine the target in law.
Rushing to find ways to spend ever-increasing sums risked skimping on value-for-money, the committee said, and accountability and could do more harm than good in some of the most vulnerable countries.
While UK aid efforts were very effective and the budget should not be cut, the House of Lords economic affairs committee said, ministers should concentrate on quality not quantity.
It also called for an "early exit strategy" for ending aid to India.
And it accused the Department for International Development (DfID) of failing to tackle fraud properly - calling the £1.2m uncovered last year "paltry and implausibly low".
International Development Secretary Andrew Mitchell hit back at the call to drop the UK's commitment to the 1970-set target to spend at least 0.7% of GDP on foreign development aid by 2013.
"The British Government makes no apologies for sticking to its commitments to the world's poorest people," a defiant Mitchell retorted - saying breaking the pledge would cost lives.
"Spending less than 1% of our national income on aid - an internationally-agreed target - will create a safer and more prosperous world for the UK."
And the peers also came under fire from development charities, one accusing the committee of being "entirely detached and out of touch from the reality of poverty in our world today".
ActionAid's Melanie Ward said: "It appears that this House of Lords Committee is entirely detached and out of touch from the reality of poverty in our world today - 0.7% is globally agreed as a fair contribution from the world's richest countries to help end poverty.
"We all made this promise and shouldn't break it now."
Global advocacy and campaigning organisation ONE said the peers were "stuck in the 1980s" and "out of tune with public opinion and out of touch with economic reality" while Save the Children chief executive Justin Forsyth said "cutting UK aid will cost lives, threatening 1.4 million children and 50,000 mothers."
"UK aid works. It is part of our DNA as a country and it is in our interest."
"The Lords' committee is wrong to call for the UK to break its solemn promise to the world's poor."
Microsoft billionaire turned philanthropist Bill Gates, whose foundation funds health and development projects, joined the chorus of criticism of the call to abandon the target.
He hailed the UK as the best in the world at targeting where it spent its aid money and said any backsliding risked undermining the "incredible progress" made over recent years.
"I'm concerned by the committee's report regarding the government's aid budget," he said.
"The UK leads the world in delivering smart, targeted aid - and I've seen for myself on the ground the incredible impact of its life-saving investments.
"Abandoning the 0.7 target risks undermining the incredible progress that has been achieved over the last several years.
"Well-targeted UK aid has helped save millions of lives by rolling back the malaria and HIV epidemics and bringing the world closer to eradicating polio once and for all. And we are on the brink of some more tremendous breakthroughs.
"I commend the UK government for its steadfast commitment to the world's poor."