DAME Eliza Manningham–Buller, the Director General of MI5 is known as a cautious person who prefers to make careful and fully substantiated assessments before speaking on any subject. So her warnings on the scale of terrorist activity in Britain, which became known yesterday, must obviously be taken very seriously. The most chilling passage in a generally pessimistic speech was this: ”The threat is serious, is growing and will, I believe, be with us for a generation. It is a sustained campaign, not a series of isolated incidents. It aims to wear down our will to resist.” That is a different picture from the one given currency at the time of the London bombings last year when the assumption seemed to be that those bombers and others planning similar attacks were mainly independent operators. But now the head of MI5 speaks of the existence of ”30 plots that we know of, often with links back to al–Qaeda in Pakistan and through those links al–Qaeda gives guidance and training to its largely British foot soldiers on an extensive and growing scale.” Speaking about the increasing number of would–be suicide bombers, Dame Eliza said they are motivated in part by ”their interpretation as anti–Muslim of UK foreign policy, in particular the UK's involvement in Iraq and Afghanistan.” Despite her care with her words they go further than Mr Blair has ever been willing to do on this sensitive issue.