No bombs were found, but the authorities had to take the threat seriously and search all the stations because four small incendiary devices had exploded in the capital on Monday. The warnings were deliberately vague following an IRA tactic first seen on Sunday when widespread travel disruption was caused in and around the capital.
The terrorists now say only that a bomb has been planted on a particular part of the network.
One call yesterday said that there was a bomb on a line between London and Sevenoaks. This meant that nearly 40 stations, including six London terminals from which trains run to the Kent town, had to be closed.
Victoria, Blackfriars, Charing Cross, London Bridge, Waterloo East and Cannon Street stations were closed for most of the morning. Some trains were stuck outside terminals for up to three hours. East Croydon station, one of the busiest junctions on the rail network, was closed by a second call, while a third shut down the Central and Northern lines on London Underground. All Tube stations intersecting with these lines or rail terminals were also closed.
London Underground evacuated 50,000 to 60,000 people from 100 Tube stations in 15 minutes at the height of the morning rush hour. About 300,000 rail commuters were either stranded in trains or found services cancelled.
While many went back home, others fought their way on to packed buses which made slow progress in traffic jams and most taxis were quickly occupied. Some passengers were involved in angry scenes with rail and Tube staff as the network ground to a halt.
It took police hours to search all the stations. A spokesman said: 'It is a very painstaking operation. We do not want to miss an inch of ground in case a bomb has been planted somewhere.'
Almost all train and Tube services were running again by yesterday evening's rush hour and a spokesman for Network SouthEast said that train services should be 'near normal' this morning.
A spokeswoman for the Association of London Authorities estimated that the chaos had cost the capital's economy pounds 34m due to lost business and working time.
However, stores in Oxford Street, in the centre of London, reported that business was only slightly down on the previous day after a slow start. Most Christmas shoppers started their journeys after the worst of the chaos was over.
On Monday, four small incendiary devices went off in the capital, two in postal sorting depots and a third at Northfields Tube station in west London. One exploded in the Travellers Tavern pub at Victoria Coach Station after being abandoned by the terrorists.
Police have appealed for witnesses who may have seen two men in their twenties, dump the black nylon holdall with multi-coloured patterns on each end in the pub at about 2pm. The bag was found to contain several incendiary devices.
People and businesses who may be targets for attacks by animal rights activists were warned to be on their guard yesterday after letter-bombs were sent to several addresses across England.
In one case, four people were taken to hospital with minor injuries and shock after a device exploded at a laboratory at Small Dole, near Henfield, West Sussex. Other devices were addressed to locations in London, Surrey, Greater Manchester and Cheshire.
Scotland Yard said the bombers were using cardboard cylinders sold by the Post Office for sending items like posters for the attacks, packing them with small quantities of 'incendiary material'.