Ambulance crews are being forced to park outside a hospital accident and emergency department waiting to deliver patients because there are too few clinical staff to receive them.

Paramedics have spent more than 140 hours in the last two months waiting outside Croydon University Hospital's A&E department.

On 280 occasions since the beginning of November ambulances have had to wait more than half an hour, figures which campaigners said could mean patients are at risk.

The figures show an alarming surge in delays since last winter, when crews were forced to wait for 30 minutes or longer on only 22 occasions between November and March.

It means Croydon NHS Trust could be forced to pay out thousands in fines if delivery times do not improve by April.

On December 13 alone, 18 ambulances were forced to wait outside the borough's hospitals for longer than 30 minutes, leaving them unable to respond to emergency calls.

The NHS Commissioning Board expects ambulance crews to hand over patients to hospital staff within 15 minutes of arriving at hospital.

It is introducing contractual fines for delays of more than 30 minutes from April, with higher penalities for delays in excess of an hour.

Croydon NHS Trust confirmed it had made improving its 'handover' times a high priority. 

London Ambulance Service said it had seen a 13.7 per cent rise in call-outs during 2012 and was working with Croydon University Hospital to speed up the delivery of patients.

The news comes after Croydon University Hospital was named as one of 17 NHS hospitals judged to have inadequate staffing lavels by the Care Quality Commission (CQC).

A report published by the CQC is July last year said the hospital did not have enough staff to ensure the safety of patients and meet their health and welfare needs.

Councillor Sean Fitzsimons, who sits on South West London Joint Health and Overview Scrutiny Committee, said he would be pressing health bosses to explain the rise in delays, which he suggested could cast doubt on plans to axe two south-west London A&E departments. 

He said: "It is a worry. Whatever the reason for the rise, I am very concerned and it is a matter that I will be pressing our scrutiny meeting to have a look at."

Geoff Martin, chair of pressure group London Health Emergency, described the figures as "deeply worrying" and warned the situation was likely to worsen if the expected closure of the   Sutton's St Helier Hospital's A&E went ahead.

He said: "It is a classic case of too much demand and not enough capacity.

"There is a huge chasm between the  demand that is being thrown at the hospital and the ability of the hospital to cope with that. That is deeply worrying and potentially life-threatening.

"The vast number of maternity and emergency cases from St Helier are going to be shifted over to Croydon and it if can't cope at the moment then it is going to come to a complete collapse."

Croydon NHS Trust said it was having to deal with more A&E admissions this winter than last year, but no figures were available.

A spokeswoman said: "Handover from the ambulance staff will only take place when the department has the physical capacity to do so and if multiple ambulances arrive at the same time sometimes this can cause a delay as we address each individual patient’s needs.

"However it is important to note that the definition of handover for this data is the time until  A&E staff take full clinical responsibility for a patient - it does not mean that patients are left in an ambulance for this period of time.

She added: "Resolving these handover issues is a very high priority for us and we are actively looking at ways to improve these turnaround times, working in partnership with the ambulance service.

"The Christmas/New Year period is always a very busy period for the emergency services.  When coupled with an outbreak of Norovirus and the impact that has on our ability to discharge patients promptly and safely, it has put the Trust under significant pressure."

London Ambulance Service received 46,201 emergency calls in Croydon during 2012 and took 35,315 patients to hospital.

Kevin Brown, the service's assistant director of operations, said: "Patient care is our number one priority and delays at hospital can mean people wait too long.

"Delays also prevent our ambulance crews responding to the next emergency. 

"We are working with Croydon Hospital so processes are in place to ensure our patients can be handed over to the care of hospital staff as quickly as possible."