Number 10 has indicated the government is set to press ahead with plans to introduce house arrest for terrorist suspects.

Speaking on Monday, the prime minister's official spokesman said that home secretary Charles Clarke had not put his proposals forward lightly.

"The control orders would allow a range of options, and at the top end, there are what everybody agrees are extreme measures, but extreme measures to deal with extreme circumstances," said the spokesman.

His comments come ahead of Friday's meeting on the issue between Tony Blair and opposition leaders Michael Howard and Charles Kennedy.

The Conservatives and Liberal Democrats have indicated their unease with some aspects of the government's proposals.

It is thought that a compromise may emerge based on greater use of judicial oversight and the possible introduction of wire tap evidence in court cases- a move backed by the Tories and Lib Dems, as well as senior police officers.

Downing Street, however, continued to downplay the latter option.

"Superficially it may seem an attractive thing, but it is not true that it would make much difference and it would do so by potentially putting at risk sources of intelligence," said the spokesman.

Continued opposition to the plans from both main opposition parties, however, could result in the government failing to get them onto the statute book.

Ahead of Friday's meeting, Home Office minister Hazel Blears refused to be drawn on whether the government is poised to reverse its plans on terror house arrests.

"We all face serious threats to national security. We need to get the legislation right," she told BBC Radio.

"That's why we are having discussions and we will be bringing forward our proposals in due course as promised by Charles Clarke."