David Trimble's post-dated letter of resignation is due to come into force on Sunday. Can the British government take any action before then to prevent his resignation?
The Northern Secretary, Dr John Reid, could suspend the political institutions set up under the Belfast Agreement in order to prevent Mr Trimble's resignation coming into force.
However, Dr Reid has strongly indicated that he will not suspend the institutions this week. He said that while he cannot predict what will happen, he will do everything "within my power" to prevent suspension.
Can Mr Trimble appoint someone to replace him as First Minister?
Officials say Mr Trimble can nominate a substitute for a six-week period which would enable the Executive to continue operating normally. His substitute could carry out all the functions of the First Minister but could not use the title. There has been speculation that he might nominate the Enterprise Minister, Sir Reg Empey, but UUP sources are playing down this option.
If Mr Trimble resigns without nominating a replacement, can Mr Seamus Mallon remain as Deputy First Minister? The First and Deputy First Ministers are elected together and are intricately linked in legislation, so Mr Trimble's resignation would mean that Mr Mallon ceases to hold office immediately. Mr Mallon will be able to continue to exercise all the functions of his office, but will not be allowed to use his title.
There is confusion over whether he will be allowed to chair Executive meetings. If he is not, the Executive will not be able to meet formally. However, there is nothing to stop Ministers meeting to discuss business as long as they do not describe it as an Executive meeting. Mr Mallon will not have the authority to nominate Ministers to attend North-South Ministerial Council meetings.
Will the 10 other Ministers in the Executive be able to retain their posts?
Yes. The Finance, Education, Regional Development, Health, Arts, Enterprise, Agriculture, Environment, Further and Higher Education and Social Development Ministers will be entitled to remain in office and carry out their functions in definitely.
Will the other Ministers want to remain in the job?
Monday's announcement by the DUP's two Ministers that they would quit the Executive if all the UUP Ministers pulled out appeared last night to have increased the possibility of a complete unionist withdrawal. Until yesterday the belief was that the UUP's three Ministers, apart from Mr Trimble, would remain in place. It is highly unlikely that SDLP and Sinn Fein Ministers would resign.
How long can the posts of First and Deputy First Minister remain vacant?
Under the Northern Ireland Act, 1998, a new election for the positions must be held in the Assembly within six weeks, creating a deadline of August 12th. If this does not happen, Dr Reid must give notice of the holding of an Assembly election.
When would this election take place?
It would be likely to occur in September or October. Dr Reid would decide on a date after consulting the local parties.
What options has Dr Reid if he wishes to avoid an election?
If Dr Reid believed a political deal on decommissioning could not be reached and the Assembly was unlikely to agree on new First and Deputy First Ministers by August 12th, he could suspend the institutions before then in order to prevent the holding of fresh Assembly elections.
If a deal was reached later and Dr Reid lifted his suspension of the institutions, the Assembly would then have to re-elect First and Deputy First Ministers after its restoration.
What will the pro-agreement parties and the two governments do following Mr Trimble's resignation?
There will likely be intensive negotiations involving the parties, the Taoiseach and Mr Blair in an attempt to reach a deal on decommissioning that would allow Mr Trimble, or any successor, to return to the Executive.
Can Mr Trimble return as First Minister?
Once Mr Trimble's resignation comes into force, he will have to face re-election in the Assembly if a deal is done and he wants to return as First Minister. The First and Deputy First Ministers will be elected together. The candidates will require support of both a majority of nationalists and a majority of unionists. The latter is not guaranteed.
The 21 DUP Assembly members, and seven other members belonging to smaller unionist parties, combine to make a 28strong anti-agreement bloc. Mr Trimble would be relying on the support of the Assembly's 28 UUP members, including the dissident anti-agreement UUP member, Mr Peter Weir, and the two Progressive Unionist Party members. Sources say Mr Weir's support is highly unlikely. He remains angry about being deselected as his party's Westminster candidate in North Down. His replacement, Lady Sylvia Hermon, won the seat.
Other defections against Mr Trimble are possible in the UUP's Assembly ranks. So even if he reaches a deal with Sinn Fein on decommissioning and wants to return to power, his reelection as First Minister is far from certain. It might even depend on the redesignation of members of the Alliance Party or Women's Coalition as "unionist". They are currently classified as "other" in the Assembly but might be willing to change if Mr Trimble needed more "unionist" votes.
What will happen the Assembly during any negotiations or stalemate?
The Assembly goes into summer recess on July 4th and is not due to meet again until September. If in September the Executive was in suspension, Assembly members would remain in office but the Assembly would not meet or carry out any functions.