Sir Reg said that Mr Durkan, who stepped down as SDLP leader on Sunday, had been a "dedicated and hard-working leader".

SDLP founder and president John Hume, Mr Durkan's predecessor as leader, also praised the Foyle MP as an "excellent legislator" who had a "huge degree of influence" both at Westminster and in the Dail.

But the Nobel Peace laureate, who is now in frail health, hinted at the decline which the party has endured under Mr Durkan's leadership, saying that he had "steered our party through difficult political times".

Mr Hume added: "He has already many achievements as MP since taking over from me in 2005 such as defeating the On the Runs Bill, changing the law to compensate the Desmonds pensioners and forcing the British Government to support the Cluster Bombs Treaty. Any one of these alone would be a huge achievement for an MP."

Sir Reg said that although he differed politically with Mr Durkan, he believed that the Londonderry politician had always put the Province first.

"I have worked alongside Mark for many years and he is one of the most hard-working politicians I know," the UUP leader said.

"I would like to place on record my sincere thanks to him in a personal capacity and also recognise the important work he has done to secure powersharing in Northern Ireland.

"While other parties refused to move forward, Mark and his predecessors have taken huge steps towards peace.

"I admit that we had our own fair share of differences in the first Assembly, however in hindsight it was a much better working relationship and alternative to what we currently have today."

Sir Reg hailed new SDLP leader Margaret Ritchie as a "talented and efficient politician".

A DUP spokesman declined to comment on Mr Durkan's tenure as SDLP leader.