40% of sites were 'defective'

Westminster City Council inspections found four out of 10 street repair sites were dangerous or defective.

It added it would also take action against the firm for failing to deal adequately with leaks and a drop in responses to emergency call-outs.

Thames Water apologised, saying contractors' performance had deteriorated, but was being checked.

It has two weeks to contact the council to agree an improvement plan.

Councillor Alan Bradley described the situation as untenable and said standards had dropped to "below the minimum expected".

We have been working closely with the council and the contractors to address this, and are determined to improve the situation Thames Water

"This is disturbing considering the potentially serious health and safety implications of poor road repairs and failure to follow basic procedures," he said.

The council has also accused Thames Water of carrying out increasing numbers of repairs early or late at weekends, when they are less likely to be overseen by council officers.

This has been denied by Thames Water, who said working at times when it is hard to inspect a site is simply a reflection of the volume of work being carried out.

Thames Water said in a statement: "We have been working closely with the council and the contractors to address this, and are determined to improve the situation."