London's already creaking transport system collapsed following yesterday's blasts, with severe delays and cancellations crippling the Tube, trains and buses.
Motorists were stuck in traffic jams as Londoners fled the city and anyone wishing to travel had to abandon public transport.
All buses within the inner zone of London were cancelled in the aftermath of the explosions, towards the end of the morning rush hour. The Underground system, used by three million people every day, was shut down completely and mainline commuter lines soon stopped running a full service.
Out on the streets commuters and tourists flooded out of Tube and train stations and formed long queues at taxi ranks.
Vehicles on the roads crawled along congested highways. Sirens from emergency vehicles rang out on the crowded streets, adding to a sense of unease and alarm. Motoring organisations described the centre of the capital as "totally gridlocked".
Travellers on the fringes of London were warned by police that they should enter London only if their journey was vital.
The suspension of the Underground led to problems at Heathrow and Gatwick airports as airlines at Heathrow warned that flights could be delayed because staff could not get to work.
Security checks caused further delays. At train stations, police and community support officers scanned concourses, shops and cafés for abandoned luggage. Several stations, including Victoria, were closed because of suspicious packages.
The RAC reported that by late afternoon, major routes out of London were jammed. On the M4, air travellers heading for Heathrow abandoned taxis and hotfooted to the airport along the hard shoulder, dragging their suitcases behind them in order not to miss their flights.
Regular searches were carried out on all buses, bus stations and garages.
On the trains, southbound services into the capital from the north terminated at Watford with no onward bus transfers. Train passengers on the West Coast main line were advised not to travel and Chiltern Railway services into and out of London Marylebone were suspended.
Some travellers were sanguine about the delays. At Liverpool Street station, Roy Hardwicke, 58, a stockbroker from Hertfordshire, said: "I'm just grateful to be in one piece."
He and 25-year-old Hannah Matherson, a headhunter, also from Hertfordshire, told how they walked out of Liverpool Street station at 8.45am, moments before the bomb blast on the underground near by.
Ms Matherson said: "I'm just glad we missed it. As long as I can get home I don't mind."
By yesterday afternoon, all mainline train stations except King's Cross had re-opened. The Tube remained shut. A spokesman warned heavy disruption was likely today.
King's Cross station will probably be shut for the next few days. A spokesman for Great North Eastern Railways said trains between the north London station and Peterborough would not be running today.
In response to the heightened concern among passengers, there will be a much larger presence of armed police at the main London terminals together with sniffer dogs and state-of-the-art equipment to detect explosives.
Last night British Transport Police (BTP), security personnel and other staff were inspecting London Underground stations and rolling stock to ensure there were no unexploded bombs.
Andy Trotter, Deputy Chief Constable of the BTP, said that while his officers would attempt to reassure people, commuters needed to be vigilant and report anything or anyone they regarded as suspicious.
Transport for London said buses should be back to normal by today. The suspended Docklands Light Railway, which takes tens of thousands of office staff to and from the Canary Wharf financial centre, is also expected to be back to normal.
The attacks illustrate the vulnerability of the transport system in big cities used daily by millions of people.
In the aftermath of the explosion, a spokesman for Transport for London said: "We are advising passengers not to go into central London." It set up a special car-share requests page on its website following "the unprecedented number of requests to liftshare".
Security experts pointed out that it would be impossible to introduce airport-type security at train stations given the number of people that use public transport in London.
Tim O'Toole, managing director of London Underground pointed out that 500 trains are in operation during rush hour. There is room for 700 people on each Circle Line train and 900 on rolling stock used on the Piccadilly route - the services targeted in yesterday's attack.
London buses make some 5.5 million journeys every day.
Just three weeks ago the G8 leading industrial nations agreed to co-operate to take measures to protect transport systems, particularly underground networks, from terrorism. The decision was prompted partly by the terrorist attack on rush-hour trains in Madrid last year in which almost 200 people died.
Meanwhile, the Royal Mail warned that postal services would be disrupted across the country over the next few days as its vehicles had been caught in the gridlock.
The Government is keen for London to bounce back from the attacks speedily. "This has been an appalling crime and a terrible tragedy, but we've got to make sure that the London area comes through this and the people are able to go about their daily lives as soon as possible," Alistair Darling, the Transport Secretary said.
Where the transport system has been affected
Most of London Underground is expected to run normally today after overnight security checks on stations and trains. It is thought, however, that there could be disruption on the northern part of the Circle Line and stretches of the Metropolitan route because of ongoing work to clear wreckage and make repairs.
There were massive jams on roads heading out of London last night. Many of those who work in London were picked up by loved ones or were given lifts by colleagues. Some workers may opt to drive into London today to avoid public transport, while others may decide to stay home.
Transport for London last night said that it could take some time to get bus services back to normal after they were suspended yesterday in the Zone One area of central London. However a spokesman said that full services should be in operation for most of today.
Network Rail plans to open all the main London stations today, although Alistair Darling, Secretary of State for Transport predicted that Kings Cross - the scene of one of the terrorist attacks - would be closed for the next few days. Fresh disruption is possible today as police react to security alerts from the public.
There was no reported disruption to flights yesterday as a consequence of the attacks and it is expected that airports will be working normally today. It is thought, however, that extra security measures will be taken with more armed police deployed to reassure passengers.
Forced to close
All West End shows were cancelled last night, including Billy Elliott, Les Misérables, and Phantom of the Opera. The National Theatre called off performances on the Olivier and Lyttelton stages. The Barbican also cancelled its events.
More than 100 schools will remain closed today because of disruption to public services. Westminster and Camden councils announced all their schools would be shut. In Islington, one third of all schools will remain closed. In Tower Hamlets, Bishop Challoners secondary school, which became an emergency centre, will remain closed.
Shops and banks in central London closed their doors early. The London Retail Consortium said that businesses had followed police advice by keeping staff indoors then allowing them to go home in the afternoon after an all-clear.
The second night of the HM Tower of London Festival of Music, with Amy Winehouse and Kyle Eastwood, was cancelled. At the Royal Opera House, a performance of Othello was cancelled. The dance band The Prodigy postponed its gig at the Brixton Academy until 7 August while the boy band Blue cancelled its appearance at the Wembley Arena.
The Queen and Paul Rodgers Hyde Park show, set for today, will now take place on 15 July. REM's Hyde Park show, set for tomorrow, will now take place on 16 July.
A London Press Club charity ball was called off last night. A Ministry of Defence spokesman said planning continued for Sunday's National Commemoration Day to mark the 60th anniversary of the end of the Second World War. He said a final decision would be taken after taking advice from police and transport authorities.
The Royal Mail said national postal deliveries would be disrupted as its vehicles were not able to move in or out of London. Around 25 per cent of the country's mail moves through London.
James SturgesReuse content