Private ambulances bringing patients to Hillingdon Hospital put a strain on A&E, a report has revealed.
A report on the hospital's performance presented to the Hillingdon Hospitals NHS Trust board of directors last month states that they can lead to "significant operational difficulties".
Figures show that on average, around one in ten ambulances that pull in to the hospital are either privately owned (between eight and 11 per cent) or from the voluntary sector (a further 1.5 to 2.5 per cent), but this can rise to as many as one in four on any given day.
Because these ambulances are not recorded on the Hospital Alert System (HAS), the Accident and Emergency department which will ultimately deal with the transported patients are not notified and cannot prepare.
The report notes that there have been instances where several non-NHS ambulances have come in within a short space of time.
The use of private ambulances by the London Ambulance Service (LAS) has boomed in recent years, due to rising demand.
A spokesman for the Trust said: "The operational difficulties referred to in February's board paper relate to LAS's use of private ambulances to transport patients to Hillingdon's A&E department.
"When an LAS ambulance is on route to the hospital they are tracked by the Hospital Alert System, which alerts our A&E department to their arrival. If LAS use private ambulances then they are not on this system, therefore there is no early warning of the arrival."
LAS has contracts with four private ambulance firms to deliver patient care when demand peaks.
Figures from April 2013 revealed that LAS spending on private ambulances rose by £3.8million in two years - from £400,000 in 2010/11, to £4.2million in 2012/13. The same trend is evident in other parts of the UK.
That same month, it was announced that LAS would receive £7.1m in extra funding to increase the number of staff.
At the end of February, the number of frontline LAS staff, including paramedics, stood at 2,413.
The LAS has responded to the concerns.
A spokesman said: "We manually track our private ambulance crews and will contact and advise them to take patients to alternative emergency departments if particular hospitals are very busy.
"We’re in contact with colleagues at Hillingdon Hospital and give them regular updates to help with their planning.
"Just like hospitals which employ more agency nurses during busy periods, we use a limited number of carefully selected private ambulance services to help us manage increasing demand.
"As we recruit more staff and modernise our service we will reduce our use of private ambulance crews."
