Ambulance crews are struggling to get to critically-ill patients quickly enough.

Paramedics are supposed to answer three-quarters of 999 calls within eight minutes but Sussex Ambulance Service averages 72 per cent.

Crews are treating more patients than ever before and the service is at full stretch.

Performance figures for all ambulance services in England in the last year have been published by the Department of Health.

Sussex Ambulance treated 664,000 patients, making it one of the busiest services in the country.

Spokeswoman Janine Bell said there had been an eight per cent increase in demand in the last year.

She said: "We know our staff deliver high standards of care and their skills and clinical equipment are increasing and improving all the time.

"Importantly, our recent patient survey showed 98 per cent of our patients are very pleased with the service they receive."

Answering 75 per cent of category A emergency calls in eight minutes is a Government star grading target and could affect the service's performance when ratings are published next month.

Ms Bell said: "We recognise how important it is for us to do this and are continuing to work hard on modernising our working practices, recruiting more staff and finding ways of appropriately managing less urgent categories of call."

Ambulance workers will be paid a bonus of £60 or £120 for each month they manage to hit the target until October.

The service is trying to ease pressures by cutting the number of time-wasting 999 calls.

These have recently included a man who cut his toenails too short and a driver who saw an injured deer in the road.

However, unions have already warned that staff are pushed to the limit and there is little room for manoeuvre if people go off sick.

Volunteer reserves from St John Ambulance and the Red Cross are increasingly being called on to answer 999 calls at busy times because professional crews cannot get to the scene quickly enough.

Unions say this will happen more frequently until money is invested in the service to bring more crews on the road.

The service deals with more than 400 emergency calls daily, rising to more than 600 during peak times.