He hit out after a TD in the Republic vowed that his party would pull ministers out of government in Stormont if no decision was taken to devolve powers.

Caoimhghin O Caolain, Sinn Fein leader in the Irish parliament, said: "If we are forced to conclude that change will not be forthcoming from the Executive then we will have no option but to pull out our ministers and seek to put pressure where responsibility ultimately lies, which is on the British Government in London."

But Sir Reg warned it would be disastrous if control was handed over – and accused Sinn Fein of trying to blackmail Ulster voters.

He told the News Letter: "The Executive cannot even fix drains to cope with floods so how can it take on responsibility for policing and justice?

"The Executive has shown it isn't capable of governing as it should yet and is not functioning as it should.

"If we can't handle the bread and butter stuff, how are we going to handle this?

"The people of Northern Ireland do not deserve to be blackmailed by claims of this type."

A bitter deadlock over the transfer of justice powers to Stormont disrupted Executive business for weeks before it broke for the summer.

Republicans and the Government wanted control handed over from Westminster in May but the DUP has resisted, concerned over how supporters would react to a Sinn Fein minister being put in charge of the police.

Sinn Fein highlighted its growing frustration in June when it threatened to break up the Executive by sabotaging the election of DUP leader Peter Robinson as First Minister when he took over from Ian Paisley.

It was only after crisis talks with Prime Minister Gordon Brown and the Irish government that the DUP and Sinn Fein committed themselves to intensive negotiations.

Speaking yesterday at a republican rally at Co Cavan, Mr O Caolain said there was still "widespread and growing concern among republicans" at the failure to transfer powers from London and said his party's patience should not be tested any further.

The TD added: "When Sinn Fein changed our policy on policing in the north, accepting that a new beginning was being made, it was with the prospect that policing and justice powers would be transferred by May of this year.

"It is now the end of August and we do not even have a date for transfer. This is totally unacceptable."

Sir Reg last night threw down the gauntlet to Martin McGuinness to clarify whether he supported the remarks.

He said: "I challenge Martin McGuinness to say whether Mr O Caolain was speaking for him.