At least three-quarters of England's ambulance trusts look set to miss a new target for the time taken to respond to life-threatening emergencies.

By 1 April, ambulances are supposed to respond to 75 per cent of urgent calls within eight minutes of a control centre worker picking up the phone. Currently, the clock starts ticking after a patient's details and location have been taken.

But figures obtained by HSJ show nine of the 12 ambulance trusts were missing the call connect target by up to 18 per cent in the run-up to the deadline. Out of nine trusts that provided information, only one is already hitting the target. Isle of Wight Ambulance Service exceeded the target in February by 0.7 per cent.

Year-to-date performance figures show East of England Ambulance Service trust is achieving 64 per cent, compared with 70.6 per cent at West Midlands.

In March, the figures were 65 per cent for London, 73 per cent for the South West, 70 per cent for the North East and 72 per cent for the East Midlands.

In February, Great Western achieved 66 per cent, while Yorkshire managed only 57 per cent in January, the most recent month for which figures are available. Yorkshire's March board papers said the trust does not expect to deliver the call connect target during the first half of 2008-09. This is due to "unavoidable delays" in delivering communication centre changes and "full road operations capacity".

North West Ambulance Service trust, which did not respond to HSJ's request in time, said in March board papers that "there is considerable risk that the call connect target will not be met by the target date of April". Performance in January was 64 per cent.

Unison ambulance national spokesman Sam Oestreicher said funding had not kept up with the 8 per cent yearly increase in calls to ambulance trusts. Starting the clock before patients' details have been ascertained risks ambulances "rushing off in the wrong direction" and being unable to prioritise the most demanding calls, he warned.

Association of Professional Ambulance Personnel spokesman Jonathan Fox said the target was "simply not do-able".

"Trusts need to ensure that IT is up to speed so they can receive and dispatch calls quickly. They also need a big fleet of response units. They're investing in these things but it's simply not enough."

London Ambulance Service trust chief executive Peter Bradley said: "We are now answering calls in our control room more quickly than we ever have done."