Britain was in the grip of a security crackdown last night after the terrorist attacks in London and Glasgow.

Up to 6,000 armed police officers were on the streets, sources said.

Jacqui Smith, the Home Secretary, told MPs that security had been tightened at more than 450 sporting venues and around 400 shopping centres across the country. Concrete blocks were set up at Wimbledon yesterday to stop anyone from ramming the All England Club. Organisers of Thursday's Henley Royal Regatta are looking at whether to move public car parks away from the Thames.

Office workers and commuters also found themselves subject to more rigorous checks.

Commuters driving into Canary Wharf in Docklands, east London, had their steering wheels swabbed for explosive residue when entering an underground car park.

Richard Kemp, the security director at Canary Wharf, said: "Searches of all car parks are being carried out on a frequent basis and police have an increased presence on the estate and are working closely with our own security staff."

Last night the Home Office issued counter-terrorism advice to businesses, which government officials said could apply to schools and universities. The advice recommended searching premises inside and out and securing emergency exits when not in use.

Staff should be fully briefed about evacuation plans and escape routes must be well defined, it said.

Workers should be told what to do if an area was cordoned off.

Airline passengers were banned from being dropped off or picked up directly outside all airport terminals.