Thames Water has pledged to replace more than 3,000km of main pipes under London despite admitting earlier this year it could cost £20 billion.

At a meeting with the London Assembly environment committee in January, senior staff at Thames Water said the 150-200-year-old pipes would also take around 40 years to fully replace.

However on October 2, Thames Water outlined its long-term strategy to replace all of the 3,200km of massive 18-inch trunk mains that act as the water motorways across the capital.

Speaking at the London Assembly meeting earlier this year, members grilled Thames Water officials on why there had been so many burst pipes across London last winter.

Multiple homes and businesses flooded, from Bexley to Wimbledon, from Lewisham to Richmond, and many more people were left without running water for several days at a time.

The water provider admitted the old pipes were struggling to cope with freezing temperatures and that they had been “devastating” Londoners lives. In one week in January 2017, 500 engineers had to repair more than 1,000 leaks.

Speaking at the meeting, Richard Aylard, director of external affairs and sustainability from Thames Water, said: “They are 150 years old. They weren’t cast to modern standards of quality control.

“They were laid by men using block and tackle and pulleys from the back of carts. Some of them were dropped on the ground.”

When asked whether it would be possible to replace the old pipes with modern, more durable pipes, Danny Leaman, head of water networks at Thames Water, said: “Our estimate at the moment is that it would probably take somewhere in the order of 40 years and cost somewhere in excess of £20 billion.”

Now though Thames Water have said they would replace these old pipes, with a spokesperson not denying the earlier stated £20bn figure, saying it “was obviously based upon a number of considerations, such as cost, typical productivity and logistics.”

Steve Robertson, Thames Water’s chief executive officer, said: “I fully understand how disruptive and upsetting these events have been for our customers and that’s why we’re determined to learn lessons.”

“We’ll be communicating our action plan with affected communities, customers and stakeholders to ensure we’re being held to the highest standards.”

Since December 2016, the company has been working to re-line and replace those trunk mains that burst, and is now starting to replace the trunk mains with the parts of the network where the risks of defects are greatest.