Prime Minister Gordon Brown said on Monday he would stick to his plan to detain terrorism suspects for longer before they are charged, despite the prospect of a humiliating defeat in parliament.

With a rebellion rumbling in the Labour Party and threatening Brown's faltering leadership, he said a plan to allow detention of suspects for up to 42 days without charge was the "right thing" to do "to protect the security of all and the liberties of each".

Brown, whose Labour Party lost a previously safe parliamentary seat last month and was beaten into third place in local elections, does not have to call a national election until 2010, when he hopes the economy will have had time to recover.

His poll ratings have fallen in recent months, eclipsing the political honeymoon he enjoyed after taking over as prime minister from Tony Blair almost a year ago.

As many as 50 Labour MPs are thought to be ready to vote against Brown's 42-day detention plan when it comes to the vote next week.

The plans, which would extend an existing 28-day limit, were attacked by the government's former top lawyer, ex-attorney-general Lord Goldsmith, who described them as a "very serious incursion on our fundamental freedoms".

Interior Minister Jacqui Smith met Labour MPs to urge them to fall in line, and suggested there would be tight limits on when the new powers could be used. But many remained sceptical.

"I wasn't convinced that the measures she was suggesting would enhance the security of this country," said Labour MP John Grogan after the meeting.

NATIONAL SECURITY

Writing in the Times, Brown said he would not give ground.

"Some have argued that I should drop or significantly water down the 42-day limit," he wrote. "But having considered carefully all the evidence ... I believe that ... allowing up to 42 days' pre-charge detention in these exceptional terrorist cases is the right way to protect national security."

Political analysts say Brown will be fighting for his political life over the next two months and may struggle to survive as party leader into the summer parliamentary recess.

Most commentators say it is most likely to be the economy, an area where he won a reputation for competence during his 10 years as Chancellor under Blair, that decides his future.

The economy grew at its slowest pace in three years in the first quarter of 2008, and inflation is forecast to rise near to 4 percent, limiting the central bank's scope for interest rate cuts.

News that Britain's largest buy-to-let mortgage lender has run into financial difficulties in a global credit squeeze - which has already contributed to the collapse of one major bank - was likely to darken the scene further.

Brown's opinion poll ratings have shadowed the economic decline. A YouGov poll in last Friday's Telegraph newspaper gave Labour 23 percent support against 47 percent for the Conservative Party.