Millions of pounds will have to be cut from NHS budgets after a massive hole was discovered in the finances of a neighbouring trust.

Independent auditors were called into NHS Croydon after a deficit of up to £25m was discovered by its financial team.

NHS Kingston will not be asked to bail out the trust but neighbouring NHS Richmond will be asked to increase the surplus it makes this year from £4.2m to £5.6m. Another trust, NHS Wandsworth, will be asked to find £14.5m, up from its original target of £12.3m.

Health campaigner Geoff Martin, of London Health Emergency, said: “In the run-up to the busy winter months, NHS Croydon patients will die unnecessarily as a result of this.

“I think the people who created this crisis and have presided over it should be forced to resign.”

NHS Kingston has been temporarily merged with Croydon, Richmond, Sutton and Merton, and Wandsworth in the run-up to spending power being fully handed over to GP commissioners next April.

A spokesman for the new organisation, called NHS South West London, admitted it had a “significant budgetary challenge” and was developing an action plan to get back into the black, using existing financial resources if possible.

The trusts are already trying to find £64.5m in savings out of their joint £2.2bn budget as part of a review of healthcare in south-west London.