Northern Ireland First Minister Peter Robinson today threatened to resign if Justice Minister David Ford allows prison reform that could remove royal insignia and titles from the region's jails.

He made clear he would take the ultimate political step of quitting the job and trigger an election if the symbolic change was enforced.

Mr Robinson told party colleagues that Her Majesty's insignia would not be removed, adding: "Not on my watch."

Mr Robinson said: "It will not happen on my watch, let's make this very clear."

He added that any change in British emblems was out of the question, and said: "It is simply not on the agenda."

The Democratic Unionist Party (DUP) leader said that if Mr Ford tied the proposed changes in symbolism to his reform programme, than the entire process could be compromised.

The Justice Minister is involved in implementing a major overhaul of the prison system, which evolved during the years of violence, and which a string of damning reports have said is unfit for the needs of the 21st century.

Last week Mr Ford unveiled a £60 million redundancy package to allow prison officers who served during the Troubles to leave the service, so new staff could be recruited.

The Justice Minister said the reform package had to include an enhanced exit scheme to recognise the service of prison staff - with 29 members murdered during the Troubles.

The redundancy scheme is only one element of wide reform which will see a major shake-up of all facets of the prison regime.

At the time the redundancy scheme was announced, officials said a reform of the service's symbols and emblems - such as uniform or badges - may also be necessary to secure cross-community involvement in a service whose uniformed officers are predominantly Protestant males.

Prison officer ranks include nearly 1,800 staff, with around 80% drawn from the Protestant community, 10% from the Catholic community and 10% of non-denominational background.

But Mr Ford has already said he would oppose a 50/50 recruitment scheme for Protestants and Catholics such as the one that was used over the last decade to reshape the police service in Northern Ireland.

Unionist members of the Northern Ireland Assembly reacted angrily last night when Mr Ford said changes to symbols would be an operational matter for those who directly run the Prison Service.

His comments came in a Stormont debate on the latest report into the Prison Service.

But unionists have reacted angrily - with the DUP leader now insisting that it is a resigning matter.

"If we are unable to block it in the Assembly, I will resign my position in order to force an election and allow the electorate to decide the issue," said Mr Robinson.

Mr Robinson said he was astonished by the proposed change in British symbols.

"I have had a series of meetings with the Prison Review Group. I have seen their report," he said.

"There was no mention during any meeting that I have had with them, nor was there any recommendation in their report, that there would be any change to either the name or to the badge.

"So this came completely out of the blue.

"David Ford has never mentioned it to me on any occasion.

"So let's be very clear, he is badly advised if he thinks that this is something that can be done in an operational manner."

Sinn Fein's Martin McGuinness shares the joint Office of First Minister and Deputy First Minister with the DUP leader, and his party told Mr Robinson to calm down over the issue.

Sinn Fein Assembly Group leader Raymond McCartney said the comments from the First Minister were "nearly difficult to believe".

"Peter Robinson needs to calm down," he said.

"Prison reform needs to be allowed to take its course without this sort of intervention.

"At this time of great economic challenges for the Executive, the people expect their political leaders to be getting on with the job, not engaging in this type of behaviour.

"We did not hear threats of resignation when the British Government removed £4 billion from the block grant.

"There are big challenges out there and threatening resignations and elections is not what people voted for last May and it is not helpful."

Leader of the Ulster Unionist Party Tom Elliott said the First Minister should concentrate on ensuring that the Assembly is working properly to meet the needs of the electorate.

He said of the possible emblem change: "I would prefer that we concentrated on making sure that it didn't happen."

But he said the Assembly's Ministerial Executive had yet to agree a Programme for Government and suggested politicians "concentrate on making sure we make this place operate, as opposed to just threatening to resign".

He said Mr Robinson had the power to prevent the symbols change under existing government powers: "If he wants to stop that, he can stop it at the Executive."

Mr Ford was elected to the position of Justice Minister following a deal between the DUP and Sinn Fein around the devolution of policing and justice powers from Westminster to Stormont.

The two larger parties effectively refused to allow each other to hold the sensitive post, but they backed the leader of the Alliance Party as an agreed candidate.

That terms under which that deal was agreed run out next year.