The utility's problems have been compounded as it is now in breach of its licence requirements, though Thames Water says it was expecting the decision.

It is now even harder and more expensive for the UK’s biggest water provider to borrow money as leading credit ratings agency Moody’s has downgraded its debt to “junk” status.

Thames Water’s parent company had already defaulted on some loan payments that make up its £16.5bn debt pile. More pressure will be put on its ability to meet debt obligations as a result of the downgrade.

The utility is in a perilous financial position, due to run out of money next May as it cannot raise any investment from current shareholders who described the company as “uninvestable”.

Water regulator Ofwat requires utilities to maintain an “investment grade” debt ranking, something Thames Water no longer has.