An Ulster Unionist assemblyman has warned that he will withdraw his support for the power-sharing executive if decommissioning has not started by the end of January.

Duncan Shipley-Dalton, who is seen as a moderate unionist and staunch supporter of party leader David Trimble, was speaking during the assembly's first meeting of the year.

The Democratic Unionist Party tabled a private members' motion demanding an immediate start to the handover of IRA weapons and it sparked a heated debate.

Mr Shipley-Dalton said his patience with the IRA was running out.

"I would be unwilling and unable to support the continuation of the institutions of this assembly in the event that decommissioning had not occurred by the end of January.

"Now, I say that as probaly one of the most liberal members you can find on this side of the house. I want to make sure that the members opposite realise the strength of feeling that exists within the unionist community."

But Sinn Fein's Alex Maskey said unionists were wrong to set a decommissioning deadline.

On Sunday, DUP deputy leader Peter Robinson said that any start to IRA arms decommissioning must be credible to the public as well as to the head of the International Commission on Decommissioning, General John de Chastelain.

He said: "We want a verifiable start to the surrender of a substantial amount of weaponry which will lead to all illegal weapons being handed over."

"We want to clearly set down the definition of decommissioning so people can understand the fudge when it comes."

First Minister David Trimble will be under increasing pressure from hardline unionists within and outside his party to hold to his pledge that IRA weapons decommissioning must start by the time his party's 860-member ruling council holds its 12 February meeting to review the issue.

The Ulster Unionist leader gave a commitment to the council in November that that he and his ministerial colleagues would resign from the Assembly Executive if the party did not agree that IRA decommissioning had commenced.

The council responded by agreeing to endorse the proposals of the ten-week Mitchell review to allow Mr Trimble to form the power-sharing Executive with Sinn Fein, the Social Democratic and Labour Party and the DUP before IRA decommissioning.

If the UUP council decides on 12 February that no IRA decommissioning has started, Mr Trimble's resignation would effectively wreck the Executive and plunge Northern Ireland into another political crisis.

A report from General de Chastelain at the end of January is expected to confirm whether or not any of the main paramilitary organisations have started decommissioning their weapons arsenals.

Hardline Ulster Unionists and the anti-Agreement Democratic Unionist Party have said weapons must be physically surrendered, while republicans are reported to favour possible decommissioning by putting weapons "beyond use" in sealed concrete bunkers.

Debate on the Patten report, which proposes controversial changes to the Royal Ulster Constabulary including to its name, badge, and size, is also likely to be heated following weekend newspaper speculation that Northern Ireland Secretary Peter Mandelson will soon announce that the report will be implemented.

The Patten report, compiled after a lengthy consultation throughout Northern Ireland and overseas, aims to encourage more Catholics to join the 92% Protestant force and make it more acceptable to both traditions.

It includes plans to cut numbers from 13,000 to 7,500, disband the 3,000-strong reserve and merge CID and Special Branch.

The Northern Ireland Police Federation, which represents rank-and-file officers, handed in a 400,000-signature petition objecting to some of the changes to Downing Street last week.

Its chairman, Les Rodgers, said officers would be "bitterly disappointed" if the RUC name was dropped.

Three ministers in the new Assembly Executive, Trade Minister Sir Reg Empey (UUP), Further Education Minister Sean Farren (SDLP) and Social Development Minister Nigel Dodds (DUP) will also take questions at the Assembly's first question time.

The 108 Assembly members will also discuss their own pension rights.