Despite the congestion charge, traffic in central London moves at just 10mph - the same speed as horse-drawn carriages a century ago.

Average traffic speed has improved by only 1.5mph since the toll's introduction in 2003, mayor Ken Livingstone has admitted before the London Assembly.

That means cars in central London now travel at the speed of a running chicken, instead of a running house mouse.

Just after the charge was brought in, traffic speed rose from 8.5mph to 11mph cutting journey times by 15%, according to Transport for London.

But when measured last year, the speed (including queueing at junctions) has come down to 10mph.

Traffic jams are not new in London. The 17th century diarist Samuel Pepys twice recorded being stuck in horse-and-carriage jams "The question Londoners will be asking themselves is whether an extra 1.5mph justifies paying £8 per day," said Conservative assembly member Angie Bray.

"Mr Livingstone originally promised Londoners that one of the key benefits of his congestion charge would be faster journey times across the capital.

"But we have all been badly let down. His congestion charge is a charge on congestion that we once got for free."