"I will not waver, I will not walk away, I will get on with the job and I will finish the work," Brown told a news conference after giving details of the cabinet shake-up. It included replacing six senior ministers who had quit their posts.
Former Jaguar machinist Bob Ainsworth, named Britain's new defence secretary in a cabinet reshuffle, has risen quietly through the political ranks. Ainsworth, 56, who was armed forces minister, effectively the number two at the defence ministry before the reshuffle, was elevated to the top job after the resignation of incumbent John Hutton.
Before entering politics, Ainsworth spent 20 years working at a Jaguar car plant in the central western city of Coventry, steadily rising up the trade union movement. He moved into the cut and thrust of local council politics in 1984, joining Coventry City Council, and becoming its deputy leader from 1989 to 1992.
A day of high political drama took its toll on some markets, with the uncertainty sending sterling to a two-week low against the euro, before it recovered some ground. The possibility of Brown's government collapsing has caused rumour and uncertainty in currency markets all week.
But there was some relief for investors that finance minister Alistair Darling was to remain in his job. The bond market was largely unaffected and the main London stock index rose 1.2 percent.
Brown's government has been under severe pressure for the past month, after a parliamentary expenses scandal exposed wrongdoing among politicians from all parties and left voters particularly angry with the incumbents. In the reshuffle, Brown had been expected to replace Darling, a close ally, but appeared to back away from that move after Darling made it known he did not want to go. In the end the shake-up produced less movement than expected as Brown kept key ministers in their posts to retain their loyalty.
While he has bought himself some breathing space, his authority has been wounded at a time when Britain is in its deepest recession in 60 years and unemployment is rising. Labour is well behind the centre-right Conservatives in opinion polls. Markets and voters are looking for strong government and clarity on when the next parliamentary election will be held. If Brown manages to survive the current crisis, it looks likely that he will wait for as long as possible before calling the next election. The deadline is June next year.
CONTINUING THREAT: Despite Friday's moves, Brown still faces a nascent revolt among Labour members of parliament (MPs), some of whom have been gathering signatures to unseat him. A change of leader would raise the prospect of a snap election in the autumn.
Alan Johnson, who Brown moved from the health ministry to the more powerful interior ministry, had been seen as a front-runner to replace Brown. His appointment to a senior position appeared to have ensured his loyalty for now. The limited personnel moves mean few abrupt changes in policy are likely, while the bolstering of Business Secretary Peter Mandelson's portfolio, giving him greater economic powers, underlined Brown's determination to tackle the financial crisis.
While the shake-up appeared to remove some of the doubt about the government's future, six ministers still quit their posts and Brown's authority may still be called into question.
One of the most serious resignations was that of James Purnell, the work and pensions secretary and a rising star within the Labour Party, seen as potential future leader. In a letter sent to newspapers announcing his resignation, Purnell made it clear Brown should go if Labour have any chance of beating the opposition Conservatives at the next election.
"I now believe your continued leadership makes a Conservative victory more, not less likely," he told Brown. "I am therefore calling on you to stand aside to give our party a fighting chance of winning."