Shoppers were today warned to expect months of congestion and delays as Thames Water begins digging up some of Covent Garden's busiest shopping streets.

The roadworks, which will extend from Aldwych to Trafalgar Square, are the latest phase of a three-year project to replace 40 miles of water pipes throughout the West End.

They are expected to affect hundreds of bars and shops as pavements are dug up and traffic re-routed.

Thames Water has already excavated large areas of Theatreland as part of its plan and the latest phase is to begin on 14 April and will run until March 2010.

The works will begin on Kendal Street, before moving towards Russell Street and Covent Garden's main Piazza and then reaching the east side of Trafalgar Square.

Thames Water is investing more than £6million in the improvements which will involve replacing cast iron mains, some dating back to the Victorian era, with plastic pipes that are more durable and flexible.

The area of work will be roughly bounded by Long Acre, Great Queen Street, Kingsway, Charing Cross Road, Trafalgar Square, the Strand and Aldwych. Jaymen Patel, project manager for Thames Water, said: "Tackling London's leakage is a priority for Thames Water, and we can only achieve this by systematically replacing all of its ageing cast iron water mains that are susceptible to leaks and bursts.

"Although these pipes have served the capital well, they date back as far as the Victorian era and it is therefore essential that we modernise the network-We have already laid more than 600 miles of new mains across London, the benefits of which are already evident with leakage lower than ever."

Thames admitted the work would disrupt tourists and local businesses but said it would prevent repair work in the future.

Mains replacement work in Long Acre is already under way, with 1,300ft of pipe laid since September last year. Works to lay the remaining 260ft of mains are due for completion in May.

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