The introduction of airport-style checks on travellers has been ruled out as impractical on a system that carries three million people a day.
But in an effort to reassure passengers, transport policeset out a series of safeguards on the Underground network last night.
Andy Trotter, the Deputy Chief Constable of British Transport Police, said there would be more "intrusive policing", with an increase in uniformed and plain-clothes officers on trains and at stations.
The number of "stop and searches" of passengers would be stepped up. Mr Trotter said: "The public want us to do that; they want more suspicious people challenged."
The use of sniffer dogs , who were last night checking the network for explosives, will be increased and the numbers of CCTV cameras across the network will also be expanded.
Police are also investigating the use of other technology, such as portable metal detecting arches and hand-held sensors that can detect explosives.
Mr Trotter said increased vigilance by the public remained the most effective weapon at the disposal of the police. "People are now so sharp about abandoned packages - this is breaking down the old [British] reserve."
Further measures for beefing up security were presented by the Association of Chief Police Officers (ACPO) in a meeting with Tony Blair. ACPO said terror suspects should be held for questioning for up to three months, arguing that the current maximum of 14 days is "insufficient" in complex terror cases.
* New York police planrandom searches of bags and packages carried by people entering the underground system. Those refusing to be searched will not be allowed to ride. Officers would not engage in racial profiling, said a spokesman, and passengers would be free to "turn around and leave".
Commuters' long journey home
Warren Street, Oval and Shepherd's Bush will remain closed today due to the attempted bombings.
There is no service today on the Hammersmith and City line. The Circle line remains suspended due to the 7 July attacks. There are limited services on the Northern line, though with no trains between Stockwell and Kennington. The Piccadilly line is closed between between Hyde Park Corner and Arnos Grove. Network Rail is running a normal service.
Millions of Londoners endured a miserable journey home last night.Parts of the Underground network were put on amber alert - the second highest - and many trains were taken to the next station, where passengers were evacuated. A dispute between Tube train drivers and London Underground caused further disruption to the Piccadilly line and the Bakerloo line between Paddington and Piccadilly. Up to 30 members of the train drivers' union Aslef refused to work, citing security concerns.
The Northern, Victoria and Hammersmith and City lines were suspended yesterday. The alert caused the closure of Great Portland Street, Westminster, Waterloo, St Paul's, Green Park and Oxford Circus Tube stations, as well as the mainline train station King's Cross Thameslink.
Only four of the 12 Underground lines are operating a normal service. The Circle line has been closed since 7 July and the central London section of Piccadilly line will remain closed for many more weeks.
The blasts caused Euston Road, Shepherd's Bush Green, and Kennington Park Road to be closed.
Midland Mainline trains were not running into or out of King's Cross while a suspect package was dealt with near the station at St Albans, Hertfordshire.
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