Image caption Peter Robinson said he was prepared to resign over the issue

First Minister Peter Robinson has warned he is prepared to resign if the justice minister forces through changes to the prison service's emblems.

David Ford told the assembly that changes in the culture of the prison service, including how it looks and operates, would have to be considered.

However, Mr Robinson said dropping the crown as an emblem of the service would not happen on his watch.

"I will resign and take this matter to the electorate," he said.

"It will be blocked, it is simply not on the agenda, and indeed, if David Ford ties this to his prison reform as something that is an inescapable part of the prison reform, then he will damage his whole project.

"I will resign and I will take this matter to the electorate and they will have their say," Mr Robinson said.

But Sinn Fein has told the first minister to "calm down" and focus on the reform needed in Northern Ireland's prisons.

Sinn Fein assembly group leader, Raymond McCartney said: "Prison reform needs to be allowed to take its course without this sort of intervention.

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

Mr Ford made his comments on Monday in reply to a question from the TUV's Jim Allister during a debate on the recent review of the Northern Ireland Prison Service.

Mr Allister said many unionists would object to the removal of the crown or the title "Her Majesty's Prison".

Jim Wells of the DUP said such changes would be totally unacceptable.

The exchanges took place took place during a debate on Dame Anne Owers' report on prisons in Northern Ireland.

It was published in October.

The report, ordered by Mr Ford, made 40 recommendations on how the Northern Ireland Prison Service could operate more efficiently.

An interim report by the same review team in February labelled the prison service as dysfunctional, demoralised and ineffective.