The US-UK extradition treaty at the centre of political salvos in Britain was on Friday attacked before the US Senate foreign relations committee by Irish-Americans concerned it would “threaten, intimidate, harass and persecute and terrorise” supporters of the Irish nationalist cause in Northern Ireland.

Tony Blair, British prime minister, has come under intense domestic pressure to secure Senate ratification of the treaty – a necessary step to it taking effect. In 2004, Britain incorporated most of the treaty’s new provisions into its own laws, expediting the extradition of British citizens to the US, but did not secure corresponding benefits from Washington.

As pressure on Mr Blair over the treaty grows, the plight of three former NatWest investment bankers extradited on Enron-related fraud charges became a cause celebre. Yesterday’s hearings in Washington came as a US judge refused to permit the “NatWest Three” to return to the UK ahead of their trial.

Separately, David Carruthers, chief executive of BetOnSports.com, who was arrested in the US on conspiracy, fraud and racketeering charges, waived his right to a bail hearing in Texas, and asked instead to have the conditions of his release discussed in Missouri, where the charges were filed.

At the hearing, committee chairman Richard Lugar and Senator Christopher Dodd heard from Irish-American community leaders that the 2003 treaty included insufficient protections against legal abuses and politically motivated extraditions; that it weakened judicial review of cases by giving the executive branch the final word on extraditions; and that it could be used retroactively to extradite people for offences committed years ago.

But according to testimony by Madeleine Morris, a law professor at Duke University, “Nothing in the proposed treaty threatens or impinges on the peaceful exercise of . . . civil and political rights.”

Witnesses from the US State and Justice departments, meanwhile, argued that the treaty was necessary to prosecute the US “war on terror”.

The foreign relations committee must now submit the treaty to the full Senate for a vote. Bill Frist, the Republican majority leader who sets the Senate schedule, said last week he wanted to ratify the treaty this year.

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