Mr Elliott has said he will not seek re-election to the position at the annual general meeting, in just over three weeks time.

In a statement outlining his decision and the reasons behind it, he said some "obstruction and hostility" began immediately following his election as leader and has been "relentless" since then.

The party's AGM is scheduled to take place on Saturday 31 March.

"It has been a great privilege for me to lead the Ulster Unionist Party. I have been given great support by the vast majority of party members, both elected and non-elected," Mr Elliott said.

The party AGM is scheduled to take place on Saturday 31 March - I have informed the party chairman that I will not be putting my name forward for consideration for the position of leader at that meeting.

Tom Elliott

"Following my election as leader, I set about improving internal party structures - since then I have amended the party rules, including discipline; significantly increased internal party communications; negotiated a move for new party headquarters and strengthened our staff structure.

"I have also been successful in leading the political field by making a start to reviewing the government structures and reducing the over-governance of Northern Ireland."

He added: "I ensured that we delivered on an Ulster Unionist Party Manifesto commitment that we would stop the Sinn Fein proposal to introduce on-street car parking charges in a number of towns throughout Northern Ireland and we further delivered on the improvement to the Coleraine to Londonderry rail line that was essential to the Belfast to Londonderry rail link."

But Mr Elliott, who has been at the centre of a number of controversies - including the moment he branded Sinn Féin supporters "scum" in an outburst during the Assembly election last May - also stated that he had not been treated fairly.

"I am also well aware that some people have not given me a fair opportunity at developing and progressing many initiatives," he said.

"Some of this obstruction and hostility began immediately following my election as leader and has been relentless since then. However I accept that is part and parcel of politics."

The out-going party leader added that he had informed the party's chairman.

"I thank all those members of the Party who have given me tremendous support during my time as leader and encourage them to show the same backing for the new party leader," Mr Elliott said.

"As I have done for the past number of years, I will continue to serve the people of Fermanagh & South Tyrone, the Ulster Unionist Party and the Assembly in my role as an MLA."

Mr Elliott took over the leadership from Sir Reg Empey in September 2010 and will continue as MLA for Fermanagh-South Tyrone.

Ulster Unionist MLA Danny Kennedy said Mr Elliott had given loyal and dedicated service.

He added: "I want to pay a warm and genuine tribute to his many fine qualities of honesty, integrity and leadership which he has displayed throughout his tenure as leader."

First Minister Peter Robinson said he had "a good relationship" with Mr Elliott during his time as UUP leader.

The head of the DUP said: "In particular, I pay tribute to his efforts to build greater unionist co-operation. I wish him well as he continues as an MLA in Fermanagh and South Tyrone."