UUP leader Tom Elliott has rebuffed proposals to wind up his own party and merge it with the Conservatives to form a new Northern Ireland Conservative and Unionist Party (NICUP).

His strongly-worded letter to the Tories marks the lowest point in recent years in relations between the two parties.

"We believe your proposals to dissolve our great party to be misguided, unworkable and completely undeliverable," Mr Elliott wrote in a letter sent to Lord Feldman, the Conservative chair, on Wednesday.

He states that it was "sent with the unanimous support of the party officers including Jim Nicholson MEP".

Mr Nicholson was the only person elected under the UUP-Tory pact known as Ulster Conservatives and Unionists - New Force (UCUNF).

He increased his vote after getting David Cameron's personal endorsement and now takes the Tory whip in Europe.

Despite this early success, UCUNF failed to win a seat in last year's General Election.

In fact, the UUP lost its only MP, Sylvia Hermon, who refused to stand as a UCUNF candidate and held her North Down seat as an independent.

In the letter Mr Elliott recalls that when he spoke at a UUP conference before this electoral setback, David Cameron had spoken of his "great respect for the Ulster Unionist Party" and "the unbreakable bond that binds us together".

Since then there have been attempts to restructure the relationship. Talks were held with Secretary of State Owen Paterson during the summer and with Lord Feldman at the Tory conference in October. Mr Elliott says that "a proposed way forward" that was discussed with Mr Paterson would have strengthened unionism throughout the UK.

These contacts culminated in a letter from Lord Feldman in November.

In it he called on the UUP and Northern Ireland Conservatives to form NICUP, which would have a similar relationship to Conservative Central office as the Scottish Tories. He stated that, while NICUP could have a local leader, there was no room for a "two-headed approach" and he wanted to set up a centre right party.

In his reply, Mr Elliott outlines the electoral and organisational strengths of the UUP.

He points out that it has MLAs in nearly all constituencies and representation on every council.

On the other hand, he writes off the local Conservatives as "an electoral non-entity".

A UUP spokesman said that the next move was up to the Tories.