The former head of MI5 has called for stricter border controls to combat the threat from terrorists.
While warning against the introduction of "draconian" terror laws such as detention without trial, Dame Stella Rimington delivered a stark assessment of the threat facing Britain.
In an interview she said the threat would last for "a generation".
"I don't think we should take a great deal of comfort from the fact that these latest bombs were botched," she said.
"Creating home-made explosives is difficult and they will get it wrong but they will get it right as well."
She contradicts repeated Government statements the invasion of Iraq has not increased the extremist threat.
"Terrorism was around from this source before we went into Iraq or Afghanistan," she said.
"But there is no doubt it has acted as a recruiting sergeant for a lot of these young men because of this sense of grievance about foreign policy."
She called for improved border checks, a demand that will resonate strongly in the light of revelations that July 21 bomber Muktar Said Ibrahim was able to attend a jihad training camp in Pakistan despite being suspected of terrorism.
She said: "We have realised that the free movement of people is a great concept but if you have people who would kill you there have got to be a lot more checks."
