An increase in the number of private ambulances arriving at Hillingdon Hospitals Foundation Trust’s accident and emergency department has led to “operational difficulties”, the trust has disclosed.

The private ambulances, used by the London Ambulance Service Trust, do not appear on the A&E’s hospital alert system, meaning staff cannot prepare for their arrival, a spokesman for Hillingdon said. In contrast, London Ambulance Service vehicles can be tracked by staff through the alert system.

An analysis prepared by the trust concluded that 8-11 per cent of ambulances were private and a further 1.5-2.5 per cent were from the voluntary sector.

“This can of course fluctuate on a day to day basis with as many as 25 per cent of ambulances being private sector conveyances,” it said.

Hillingdon’s February board papers state: “There are occasions when a number of private ambulances arrive within a short period of time. This can mean during these periods a significant percentage of the ambulances offloading come from the private sector. As the department has no early warning of these arrivals, it can cause significant operational difficulties.”

A spokeswoman for London Ambulance Service said: “Just like hospitals which employ more agency nurses in the winter, we have been using 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.”