Reid said that the existence of so many plots means that the police and MI5 are fully stretched and cannot divert their precious counter-terrorism resources to a lengthy public inquiry into last year’s London suicide bombings.

Reid revealed the existence of the plots — far more than have previously been reported — at a meeting with some of the victims’ relatives and survivors of the attacks last week.

He failed to give further details but the claim appears to fit in with briefings by MI5 which suggest that as many as 1,200 potential terrorist suspects may now be in the UK.

One of the operations is thought to have been the target of raids by hundreds of police officers last week. Anti-terrorist police believe they may have thwarted a wave of suicide bomb attacks on British and US forces in Iraq.

The police arrested eight men during the armed raids. The men, all from Libya, were being held on suspicion of encouraging and financing Al-Qaeda operations abroad.

Sir Ian Blair, the Metropolitan police commissioner, has said previously that security services have foiled three attacks by Al-Qaeda terrorists since the July 7 suicide bombings. Reid may also have been including at least three more alleged plots where charges are current.

That still appears to leave a further 13 current Islamist plots which, on Reid’s account, are under investigation.

Experts say that such a figure is far higher than Whitehall security officials have previously admitted.

Officials at the meeting also told relatives they had recovered CCTV footage of the bombers on the trains, as well as “post-explosion” images.

However, a senior official from the Home Office’s counter-terrorism department said that it had decided not to disclose that footage because it was “disturbing”.

The 20 survivors were also told that although there is a review into the level of compensation for victims of atrocities any increase would not apply retrospectively, so would not cover those caught up in the July 7 explosion.

Reid said this was because such an exemption would mean having to give extra money to casualties of the IRA’s bombing campaigns and the government had insufficient funds.

Rachel North, a survivor who was present at the meeting with Reid, said: “We asked the home secretary to initiate a public inquiry and he said he could not divert police and intelligence resources from tackling 20 major conspiracies they are now investigating.

“I don’t know whether he meant to say it, but he did. He was very clear about the extent of the threat.

“He asked how we would feel explaining to the families of future bomb victims that our insistence on a public inquiry had drawn away vital police resources, which was a bit of a low blow really.

“He kept referring to the Bloody Sunday inquiry as an example of how public inquiries can drain resources. That is an extreme example and somewhere in the middle there must be something appropriate.

“We need a public inquiry to understand what happened and look at the issues transparently and honestly,” North said. “Defeating terrorism is not just about responding. It is also about looking at the bigger picture and grasping why it is happening.”

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