The health regulator has opened an investigation into excessive A&E waiting times and a multi-million-pound financial deficit at Kingston Hospital.

Money troubles could threaten the hospital's sustainability, Monitor warned today.

The regulator said it was concerned "because some patients are waiting too long for A&E treatment and the trust is predicting a £8.8m deficit for this financial year."

The number of people seen within the national four-hour waiting time target for accident and emergency departments has been slipping since October last year, Monitor said.

It added: "The scale of the deterioration in Kingston’s financial position may force the trust to apply for additional funding."

The foundation trust's finances have been in trouble since at least the beginning of this year.

When then-Liberal Democrat leader Nick Clegg visited ahead of the general election, chief executive Kate Grimes said her team was "struggling" to pare back what she called an already highly-efficient service.

A number of departments were "significantly under-funded", she added.

Mark Turner, Monitor regional director, said: "Some patients of Kingston’s have been waiting too long to be seen in A&E.

"This situation needs to improve. Kingston also seems to be experiencing some financial challenges which may risk its long-term sustainability.

"We have launched this investigation to find out more about both situations and to establish what can be done to help the trust improve things."

A hospital spokeswoman said: "Kingston Hospital has managed its finances very well for many years and we have some of the best clinical outcomes in the country.

"But, in line with the rest of the NHS, the amount we are paid for each patient is reducing and we have also absorbed some costs that were previously paid for nationally.

"As a result of setting the deficit budget, Monitor has already spent some time with us looking at our financial plans and performance and we very much welcome this next step to investigate in more detail some of challenges we are facing.

"The trust takes extremely seriously the need to ensure patients are seen and treated within the four-hour A&E target.

"Over recent weeks our performance has started to improve and, to ensure that we continue to sustain improvements and can consistently meet the target, we have implemented a transformation programme.

"We are already working closely with our community and CCG partners to ensure that patients are being discharged in a timely fashion."

Kingston and Surbiton MP James Berry said: "Everyone in Kingston is entitled to expect to be seen in A&E in less than four hours. That's why there's a target. I'm sure the Monitor process will help them.

"The hospital being in deficit isn't a cause for massive alarm, because it's not affecting front-line services. There are numerous hospital trusts in the country who are projected to run budget deficits.

"We are investing £10bn in the NHS. If the government is providing exactly the funding the NHS has asked for, NHS hospitals and foundation trusts that control their own budgets shouldn't be running deficits.

"If there was any threat to Kingston Hospital then both Zac Goldsmith and I would be the first people on the barricade.

"There's no suggestion whatsoever of any threat. It's not about the future of Kingston Hospital in terms of closure.

"We, as a community, need to get behind the very dedicated and hard-working staff. This is going to be a knock to their morale. I see the really great work they do."