There has been greater vigilance at key sites such as the City and the Canary Wharf complex in London, and military installations across the country. Senior politicians in Northern Ireland and at Westminster have been warned they could be assassination targets.
And in recent weeks security has also been increased at potential targets in Northern Ireland, including Belfast International Airport.
The threat was underlined when the IRA tried but failed last Wednesday to blow up a security forces vehicle in Belfast with a Semtex mortar.
This week, the head of Scotland Yard's Anti-Terrorist Branch, Commander John Grieve, warned of these "dangerous months" and urged people to be on their guard.
"Unfortunately, it is a reality of life that we need to be continually aware of the threat of terrorism, particularly from the Provisional IRA," he said.
Police forces across Great Britain are also showing extra vigilance. A spokesman for Greater Manchester Police, which had to deal with a huge IRA bomb last June, said it was deploying a "high-profile" police presence to reassure the public.
Tony Blair, on a visit to Ulster yesterday, emphasised that he would not play politics with the peace process and he promised that when in office he would be "straining every sinew" to move it forward.
Ministers believe the IRA will put off a renewal of the ceasefire until days before a general election to put the maximum pressure on a possible incoming Labour government. They are convinced that hopes of an extended Christmas ceasefire will be dashed by the IRA. One minister said: "They have become highly active and are clearly planning attacks."Reuse content