The UK should put on hold controversial extradition laws which allow fast-track removals to the US, Liberal Democrat leader Sir Menzies Campbell has said.
The NatWest executives say they should be tried in the UK
Sir Menzies said the 2003 Extradition Act was a "constitutional disgrace" given that the US Senate had yet to ratify the treaty behind the laws.
Three UK bankers, who deny guilt, are wanted in the US over Enron. They are due to be extradited this month.
The government denies claims that the extradition arrangements are one-sided.
The extradition laws have faced criticism because they do not require the US to provide "prima facie", or solid evidence of wrongdoing, to extradite a UK citizen.
Until it is ratified in the US, Britain however must still provide the US with evidence of "probable cause" if it wishes to extradite someone from the US.
The Extradition Act was established in the wake of the 11 September attacks in 2001, and was intended to accelerate the extradition of terror suspects.
But is has been the centre of controversy following the decision to use it for non-terror related allegations.
Sir Menzies said the arrangements were not reciprocal and were a "piece of ineptitude" by the UK Government.
"We have this extraordinary situation in which we essentially have a unilateral treaty," he said.
"Both countries signed this treaty, Britain has ratified it, we've changed our domestic legislation so that it conforms to the treaty.
"But in the United States, the Senate, largely under the influence of the Irish lobby which is determined to prevent any question of suspected IRA terrorists being extradited back to the United Kingdom, simply refuses to sign."
Sir Menzies said ministers could pass a new law to suspend the extradition obligations until the US Senate ratified the treaty.
The act is being used to extradite NatWest executives David Bermingham, Gary Mulgrew and Giles Darby.
This month they failed in an appeal to the European Court of Human Rights for the extradition to be postpone.
The Home Office said the bankers' lawyers had argued that the men should not be extradited as their alleged offences were mostly committed in the UK.
But that argument had been rejected by the courts, who had upheld the home secretary's decision to allow the extradition, said a spokesman.
He insisted the extradition obligations were not "unbalanced".
"That was the case but the new arrangements have redressed this," said the spokesman.
"The US has always required all extradition requests from any country to show probable case.
"In practice, this differs very little from our term: 'information which would justify the issue of a warrant for the arrest of a person'."
The UK required from America information of a similar standard to that needed from most European countries, he added.