"Mr Blair is the most qualified person on earth to resolve the Middle East issue"
Dave, London, UK
Send us your views
He was reported to be sceptical of Blair's decision to go to war in Iraq and is said to have disapproved of the former leader's refusal to call for an immediate halt to last year's war in Lebanon between Israel and Hezbollah.
Alistair Darling, one of the most experienced ministers in the government, was appointed as finance minister.
Darling, who takes over the role of finance minister from Brown, was close to Blair and served under him for all 10 years of his premiership.
But Robert Peston, Brown's biographer, has described Darling as "one of Brown's oldest and most loyal political friends".
The Guardian, a British newspaper, called him "the ultimate grey man".
He inherits an economy with a less rosy outlook than when Brown held the post, with interest rates on the rise amid growing inflation.
Des Browne, who survived pressure to resign earlier this year after allowing British sailors who had been detained by Iran to sell their stories to the media, remains as defence minister.
The new cabinet also includes Jacqui Smith, one of the 101 women elected to parliament alongside Blair and later termed the "Blair babes", as home secretary.
The first woman to hold the position, Smith replaces John Reid, the former home secretary.
Jack Straw, who had served under Blair as home secretary and then as foreign secretary but was later removed from office, returned under Brown's new cabinet as justice secretary.
Mark Malloch Brown, a former deputy secretary-general of the UN, was appointed as minister for Africa, Asia and the UN.
While Brown spent his first day as prime minister, Blair was again questioned by police investigating allegations of illegal party funding.
Police would not confirm whether the former prime minister had been interviewed.
Since March last year, detectives have been investigating whether political parties nominated people for peerages, which come with seats in the House of Lords, the UK parliament's unelected upper house, in return for cash.
Blair has been questioned twice before as a witness, the first serving prime minister to be quizzed in a criminal investigation.
Prosecutors are considering whether charges should be brought against individuals involved in the probe, which cast a shadow over the final months of Blair's premiership.
Detectives also investigated whether members of Blair's inner circle concealed evidence from police.
Three people remain on police bail, two of them close aides of Blair, under suspicion of taking part in a cover-up.
All those questioned in the probe deny any wrongdoing.
After leaving the post of prime minister, Blair was appointed as envoy for the Quartet, a group of international powers made up of the US, United Nations, European Union and Russia, engaged in negotiations in the Middle East.