Gordon Brown is "without doubt the strongest candidate" to be the next Labour leader, the Lord Chancellor has declared.
Lord Falconer said the Chancellor's achievements put him "head and shoulders" above any other possible contenders to succeed Tony Blair.
The Prime Minister has said he will step down this year and Mr Brown is the overwhelming favourite to replace him in 10 Downing Street.
However speculation continues over a possible rival bid for the top job from Blairite Home Secretary John Reid.
Asked about Mr Brown's leadership ambitions, Lord Falconer told GMTV's Sunday programme: "He is an absolutely towering figure in the Labour Party."
In the interview to be broadcast this weekend, he added: "He is the person, along with Tony Blair, who has most contributed to what the Labour Government has done over the last nine-and-a-half years.
"He is head and shoulders in achievement, above anyone else within the Labour Party. He is without doubt the strongest candidate to be leader."
A Brown leadership was "the most likely course" for the party, he said, although he did not rule out other possibilities.
Asked if he was formally backing the Chancellor, he said: "Once he became the Prime Minister, or leader of the party, of course he would have my backing. "I don't know what's going to happen between now and the time that he actually takes over, which I think is probably the most likely course."
Lord Falconer, a close friend and former flatmate of the Prime Minister, confirmed that he had talked to him about his retirement plans. But he said he had "no idea" when Mr Blair would quit and didn't know whether he had picked a date.
