paramedics are sent to a 999 call as soon as the reason for the call is discovered, says Hereford and Worcester Ambulance NHS Trust .

The move comes after the BBC Radio 4's Today programme reported yesterday that ambulance trusts throughout the country were using widely different ways of measuring the time they take to respond to emergency 999 calls.

In 2001, the Government set a target for ambulances to reach 75 per cent of life-threatening emergency calls within eight minutes.

But the Today programme said it had seen evidence showing that some Trusts were achieving the target by delaying starting the clock ticking until after receiving a call.

Jenny Procter, spokesperson for Hereford and Worcester Ambulance NHS Trust, said call handlers ask for the address where the ambulance is required, confirm the phone number, and then ask 'can you tell me what's happened'.

"At the point at which they have that information the clock starts ticking," she said.

Listeners to the Today programme will also have heard a bizarre claim that the Trust responded to 349 of its 40,595 calls in 2001-02 within one second.

"Occasionally it will take someone a long time to give us the details of the complaint - if they are distressed or unsure of details," Ms Procter said.

"But because we have the address, we will already have dispatched the ambulance, and it can be on scene while they are still making the call."

She added other reasons why the response time could be listed as under a second are if:

l Ambulances are on standby in areas that, statistically, it is expected the next call will come from.

l A crew may come across an incident before 999 is dialled.