Mr Bush, who left office last year, has directly intervened in the Northern Ireland issue by pleading with David Cameron, the Conservative Leader, to urge Ulster Unionist Party to vote for a crucial policing deal.

The Irish lobby on Capitol Hill are said to be concerned the party will vote on Tuesday against the devolution of policing and criminal justice powers to Belfast.

Despite the international pleas for it to support the deal, party officials said they would not endorse the hard-fought agreement struck last month to transfer sensitive policing and justice powers from Westminster to the British province....