Tony BlairIn London. (Reuters)

London, Oct. 2 (Reuters): British Prime Minister Tony Blair was back at work today after successful heart surgery but his vow to hold on to power for five more years has sparked fevered speculation about who might succeed him and when.

Blair left his Downing Street office in the morning for Chequers, his official country residence, where his spokesman said he was due to do some paperwork over the weekend. The secluded mansion is a far cry from Westminster, which was abuzz with gossip over the future shape of British politics.

Finance minister Gordon Brown has long been seen as the Prime Minister?s heir-in-waiting but Blair?s decision to seek a third full term in office, announced out of the blue on Thursday night, would appear to have dented his chances.

In theory, Blair could now be in power until 2011, when Brown will be 60. By then, other, younger, candidates will have staked their claims for one of the world's most demanding jobs.

Newspapers said Brown was kept in the dark over both Blair?s ?full third term? decision and the fact the 51-year-old Premier was about to go into hospital for a heart operation. Brown supporters said the finance minister only heard of Blair?s plans when he arrived in Washington for a G7 meeting on Thursday, just hours before Blair told the nation.

?I can?t believe he?s done this,? the Guardian newspaper quoted one Brown aide as saying. ?It?s like an African coup. They waited until he (Brown) was out of the country.?

Some Brown supporters say Blair has reneged on a supposed deal made back in 1994 to hand over power in his second term.

British Prime Ministers are elected for five-year terms but can ? and often do ? return to the polls before their time is up if they think they have a good chance of winning. That means no one knows exactly when Blair will call the next election and, if he wins, how long his third term would be.

Blair is expected to go to the polls in May and according to his supporters is sincere when he says he wants to lead the country for another five years after that. ?What Tony Blair wants to do is serve that full third term, so all this discussion of labour leadership elections in five or six years time ? this is frankly becoming ridiculous,? said Labour election strategist Alan Milburn, a staunch Blairite seen as Brown?s main rival to succeed the Prime Minister.