BRITAIN'S water supply could be the next target for the terrorists, police warned last night.
Security at water companies and reservoirs is being stepped up after warnings that Al Qaeda's terror cells could turn to chemical weapons or poison or contaminate the nation's water supply.
Police are also concerned that terrorists will seek to disrupt power supplies by attacking or interfering with gas and electricity companies.
Water, gas, electricity and telecommunications are all part of the critical national infrastructure and are well protected against sabotage.
But concern is mounting that terrorists unknown to the authorities - like the four London suicide bombers - could have passed security vetting and taken jobs inside water plants, giving them the opportunity to release poison or other contaminants into the water supply.
A senior police officer told the Sunday Express: "Clearly these terrorists want to kill large numbers of people and the best ways of doing that are either by targeting bombs on public transport or delivering an attack on water supplies."
The officer, who did not want to be named, said: "The main concern is the water companies because if water is contaminated it will kill lots of people very quickly. My biggest concern at the moment is that we are struggling to get the water companies to take on board what needs to be done.
"We are pushing water companies to increase their security measures, but I am not convinced that they are fully acknowledging the scale of the threat."
Senior officers have been warned against expressing their fears because of concern that they might start a panic and that this may suggest a new tactic to terrorists.
But Dr Shane Brighton of the homeland security and resilience department at the Royal United Services Institute, said: "The safety of water supplies has been and remains a concern.
"Utility companies will be receiving security advice from the National Security Advice Centre at MI5. There are issues about the vetting of employees, especially since those involved in the London suicide bombings were "clean skins" unknown to the authorities.
"The basic level of security clearance doesn't involve any serious investigations into someone's background, only proof that they have no criminal record."
And Professor John Henry, a toxicology expert at Imperial College, London, said: "People can easily pass security vettings and someone who works in a trusted position can do terrible things.
They can infect water with typhoid or cyanide or botulism and you don't need a large amount."
Patrick Mercer, Tory spokesman on homeland security, said: "Our utilities are tempting targets. I hope that the concerns of the police are listened to."
Barrie Clark of the water industry body, Water Voice, said: "Every possible measure is taken to ensure customers have a safe supply. We keep a continual close watch on all aspects of security. We work very closely with the security authorities and the Government on this issue and are constantly vigilant."
The police are also on alert for a chemical strike in the light of new intelligence. In the latest attack last Thursday, police officers wearing protective suits were seen going in to Warren Street Tube station, one of the bombers' targets.
Security service operatives have also seized at least two Al Qaeda manuals giving details of how postgraduate students with specialist skills are being recruited to cook up potentially lethal chemical recipes. These books, and others found in raids in the US, as well as in London and Manchester, could hold clues to terrorist plans.
Experts from the Ministry of Defence Science and Technology Laboratory at Porton Down have so far been unable to identify the explosives used in the bombs on July 7.
Forensic officers are also still analysing liquid and solid material found in the bath of a bombmaking factory in Leeds more than two weeks ago. A source said: "We have never seen anything like this before. We can't move it for fear of it exploding."
In London, the Home Office is evaluating a pilot scheme to provide a rapid assessment of major incidents. A vehicle fitted with the latest equipment including protective suits is on call staffed by a four-strong team including police, fire and ambulance staff.
A senior intelligence source said: "The world changed on 7/7 for the UK, everything is different.
A chemical attack is still a real threat."