Taxpayers have so far forked out an additional £8m this year to hit a target of reaching 75 per cent of emergency calls within eight minutes.

Now plans are being drawn up to pump in a further £8.5m amid concerns the poor performance is reflecting badly on overall NHS ratings of services in the region.

Latest figures reveal 68 per cent of calls between April and October were reached in eight minutes.

Ambulance crews reached 76.2 per cent of casualties within the standard in September but only after managers were handed front-line roles and staff training was cancelled.

Performance worsened again last month to 72.1 per cent.

Huge difference across the region remain with just 63.3 per cent of the sick and injured reached last month in eight minutes in Kirklees and 65.5 per cent in Calderdale compared with 88.5 per cent in Hull.

Only two areas – Hull and Barnsley – met the 75 per cent target in October.

Ambulance chiefs blame the difficulties on higher-than-expected numbers of 999 calls and front-line staff shortages.

Halifax Labour MP Linda Riordan last night said the problems had been going on for "too long" and must be sorted out. "We're talking about life and death situations," she said. "If people suffering strokes and heart attacks get drug treatment quickly then it can make all the difference.

"Primary care trusts must increase funding to the ambulance service and get these problems remedied quickly."

David Bolam, who represents patients with the Yorkshire Ambulance Service (YAS), said standards of clinical care were improving but he doubted if the response time target would be achieved by March.

"They've put in a lot of money and a large number of extra staff – the problem is the targets are so difficult to achieve," he said.

The Healthcare Commission last month rated YAS "weak" for the quality of its services for the second year running.

A key review of the organisation carried out in May led to 25 recommendations for change to improve response times by September. Those included offering staff including managers incentives to work extra shifts and in some cases even responding from home to emergencies, as well as contacting retired staff to see if they would return to work.

But improvements have not been sustained and health chiefs do not expect ambulance services to hit the target until March at the earliest.

Rhys North, director of finance at Bradford and Airedale PCT, which represents Yorkshire's PCTs over ambulance services, said steady improvements in the response time target had been made since April, when it stood at 61.3 per cent. "We are in discussions to agree how this level of performance can be maintained and improved.

"We would expect YAS to deliver ongoing improvement and performance in 2009-10 and will work closely with them to monitor this."

Ambulance chiefs have struggled to achieve the target after a new standard was introduced in April measuring response times from the moment callers ring – although it has been hit by most other ambulance services around the country.

Using the old measure, 82.1 per cent of 18,000 999 calls were reached within eight minutes last month compared with 73.7 per cent a year ago.

Chief executive of YAS Martyn Pritchard said the additional cash had been spent on extra staff and vehicles and major improvements to 999 communications centres.

"We are reaching patients quicker than ever before and the public is benefiting from a better service from YAS. Significant improvements in performance have been made despite increased demand."