However, some aspects of the UUP-Tory link-up will have to be finalised early next year, for administrative reasons.

UUP executive members met at the Stormont Hotel, Belfast, on Thursday night and endorsed a pact with David Cameron and his party.

The deal – which could be the defining moment of a new era in local politics – is not a full merger.

But it is an alignment which sees the parties establish a joint central committee and proposals to fight elections together.

The key administrative issue is what name the parties will use on the voting slips.

The News Letter understands suggested titles to appear on any polling paper have been queried by the Electoral Commission, which is acting under very stringent election laws.

But, while this matter is to be cleared up, it is now expected that Tory leader David Cameron will formally unveil the deal at the UUP conference on December 6.

And he will also declare an end to the Conservatives' neutrality of recent times by saying, "I am a unionist".

An Ulster Unionist Party spokesman said the Executive Committee of the UUP has "overwhelmingly endorsed" the creation of a partnership.

He added: "The Conservative and Ulster Unionist Joint Committee will bring forward proposals on manifesto commitments and the branding of candidates, ensuring that the heritage and appeal of both parties are respected."

The spokesman also vowed the "popular appeal to the whole Northern Ireland electorate" would be maximised.

The News Letter has been briefed that the outline of the agreement is:

- the parties will not merge and will keep their current legal status and constitutions entirely intact;

- instead they will form a joint committee of the centre, to agree and oversee matters of cooperation;
- the committee will be made up of a small but equal number of UUP members and Tories;

- it will be the joint decision-making body and point of contact and votes will be carried by consensus;

- if it cannot agree, the contentious matter of debate will pass to the party leaders;

- the parties will appear together on the ballot paper and mount a joint campaign at the European election next June;

- any judgment on whether the arrangement will then extend to General or Assembly elections will be made thereafter;

- if the pact continues, it is envisaged UUP MPs would probably take the Tory whip at Westminster, after the next General Election.

It remains unclear, at this stage, how future candidates will be selected at elections.

UUP MEP Jim Nicholson is already selected and for five years has sat in the Conservative grouping in Brussels – so he is a natural choice for a joint ticket.

It is also not established how far the Conservatives would go in funding and resourcing the elections.

Or where any proposed unionist (DUP-UUP) deal to run single candidates in South Belfast and Fermanagh and South Tyrone would stand in the context of the Tory aspiration to stand candidates in every constituency in the UK at a Westminster vote.

What is clear is that the deal is not a merger but an electoral pact which has at its core something more solid, in the shape of the joint committee of the centre – forming a base for developing cooperation, if both sides wish to progress.

While neither party would be rebranded or lose its constitutional identity, their very association would create joint and separate new images.

One imponderable is how the UUP's North Down MP, Lady Sylvia Hermon, will view the deal. It is thought she is not keen to take the Tory whip – as Tory politics would not be her natural territory.

However, the delay in any decision on the Westminster whip and her loyalty to the UUP would certainly ensure she remains in the party for the time being.

DUP MP David Simpson last night called upon Sir Reg to clarify whether "his own political survival is more important to him than advancing the cause of unionism at election time", via the Tory link-up. His point was "the position of the Tory leader (David Cameron] could not be more clear; that he wants to fight every single Westminster seat in Northern Ireland come the next election".

"This raises a serious question for Reg Empey. Will he do what he is told by Cameron if his party merges with the Tories and fight all of the 18 Westminster seats in Northern Ireland?"

This would then, Mr Simpson suggested, possibly allow Sinn Fein and the SDLP to retain Fermanagh and South Tyrone and South Belfast, respectively, at the next Westminster poll.