Former prime ministers Gordon Brown and Tony Blair led tributes to former Labour energy minister Malcolm Wicks, who has died at 65.
Mr Brown called the Croydon North MP, who had been fighting cancer, a "great thinker, writer, campaigner and parliamentarian", while Mr Blair said he had "complete integrity in all he did".
Labour leader Ed Miliband praised him as a "thoroughly decent, intelligent and compassionate man" whose death yesterday left a "huge hole" in the party.
"He was a brilliant energy minister, he was a deep thinker about welfare and pensions, and Labour to his core," Mr Miliband said.
"Malcolm was also a dedicated constituency MP, always putting the needs of his Croydon constituents first. He was a brilliant campaigner.
"The way he handled his illness tells you everything about the man. He showed huge dignity and also kept on thinking, writing and advising right to the end.
"I have lost a wise confidant and most importantly a dear friend and the Labour Party has lost one of its sharpest thinkers. Our thoughts go to Malcolm's wife, Margaret, and his family."
Piers Hopkirk reports:
Mr Wicks represented Croydon in Parliament for two decades, and held a variety of ministerial briefs under Tony Blair and Gordon Brown - including pensions, science and energy.
The married father and grandfather stepped down from the government in 2008 and spent two years as the prime minister's special representative on international energy issues.
He was also made a member of the Privy Council.
Mr Wicks was re-elected with an increased majority of nearly 16,500 at the 2010 general election.
He is understood to have been unwell for some time.
Former Labour prime minister Gordon Brown said last night: "Tonight we mourn the passing of Malcolm Wicks, who was a great thinker, writer, campaigner and parliamentarian.
"He was a passionate advocate of social justice, a conscientious constituency MP and a great minister in the Labour government.
"I talked to him during his long period of ill-health and I marvelled at his courage and tenacity in fighting his illness. He will be sorely missed and our thoughts are with his family."