The death penalty was abolished for murder in the UK in 1965
The UK would not send people to the US under new extradition measures if they might face the death penalty, David Blunkett has promised.
The home secretary gave the pledge on Saturday after signing a new extradition treaty with US Attorney General John Ashcroft last week.
British objections to the death penalty, which was abolished for murder in 1965, are seen as a possible bar to UK troops in Iraq handing over senior Baath Party officials to the US.
The UK has long refused to extradite criminal suspects to states which use torture and execution.
Mr Blunkett was asked on BBC Radio 4's Today programme what would happen if the US asked the UK to extradite a suspect who could face a death sentence.
He replied: "They wouldn't be sent. I am absolutely clear.
"Whatever some of the very far liberal wing believe of me, I don't believe in the death penalty. I don't believe we should have any truck with it.
"We are very clear about this, and John Ashcroft, the Attorney General, understood that when he signed the new extradition treaty with me."
Mr Blunkett said there was no danger that American authorities could add extra charges which did carry the death penalty after extradition had happened.
"They give guarantees and we believe their guarantees."
The current UK Government has appealed for mercy in some cases of Britons on death row in some American states.
Tony Blair intervened to no avail before the execution of Tracy Housel last year.
And Foreign Secretary Jack Straw urged clemency before British-born Jackie Elliott suffered a lethal injection for rape and murder in February this year.
The new extradition treaty agreed by Mr Blunkett and Mr Ashcroft replaces an agreement ratified in 1976.
It is designed to bring extradition to the US more in line with arrangements with other European countries.
Prima facie evidence will no longer have to be put before the courts in US-UK extradition cases.
But there will still have to be a detailed statement of the facts in the case, which concern a crime carrying at least a year's jail term in both states.
Mr Blunkett said: "This new treaty will mean much closer co-operation and cut out much of the paperwork which has led to unnecessary delays in the current system."
Such problems had allowed criminals to exploit loopholes in the system.
America is the UK's biggest single extradition partner. The Home Office says it takes on average a year to extradite somebody to the US.