Lives are being put at risk because ambulance crews are not answering 999 calls quickly enough, staff have warned.

The claim comes as figures show Sussex Ambulance Service responds to 61 per cent of emergency calls within its target of eight minutes.

The figure is well below the recommended level of 75 per cent for British crews, which the service hopes to reach by the end of March.

Ambulance chiefs said the main obstacle to reaching the target was the difficulty of recruiting crews.

The service employs 410 paramedics who deal with more than 500 call-outs a day. Operations director Trevor Anderson said another 70 paramedics were needed.

He said the Brighton and Crawley areas had been particularly affected by the recruitment problem.

Mr Anderson said: "The problem in Brighton is probably because of the high property prices in the area and the fact that a lot of people commute from there to London.

"Crawley has very low unemployment because of Gatwick Airport, so it is hard to get staff.

"We can try to do things like bring in more ambulances, but if we can't get the staff to use them then we are still going to have the basic problem."

Mr Anderson said the service was working to improve response times and the figure was an improvement on last year, when it was only able to respond to 56 per cent of calls within its target time.

He said only four services out of 36 nationally were operating at a 75 per cent level.

A spokesman for public service union Unison said: "People are working extremely long hours, often without a break, to cope with demands, which has led to some people leaving.

"People leaving means a shortage of staff and makes things more difficult. It is a vicious circle.

"A lot of people within the service are saying that lives are being put at risk because we are not getting out to people as quickly as we should."