North West Ambulance Service trust has admitted it can only afford to buy 35 of the 128 ambulances it needs to replace, raising questions over the reconfigured service's buying power.

Board papers from the service, which was formed in July 2006 following the merger of four trusts, say it needs to replace 128 vehicles in 2007-08, more than a third of the 345-strong fleet.

But due 'to the major capital and revenue impact' of replacing even the most urgent 50, only 35 new vehicles will be bought this year, it says. It means 138 more ambulances will need to be bought in 2008-09.

Unions claimed the admission cast doubt over whether last year's reduction of 29 English ambulance trusts to 13 was giving the new organisations better strategic capacity, as promised by the Department of Health.

The trust said it had inherited the problem from predecessor organisations Mersey Regional Ambulance Service trust, Greater Manchester Ambulance Service trust, Cumbria Ambulance Service trust and Lancashire Ambulance Service trust.

Craig Wilde, North West Ambulance Service Unison branch secretary, said he was 'gobsmacked' by the figures.

'We were told that with the merger comes increased buying power. We are such a large trust now. We could afford [to buy new ambulances] when we were under Greater Manchester Ambulance Service so why can't we afford it under NWAS?'

Ambulances nearing the end of their lives would need more maintenance, he said, meaning crews faced having to 'root around for a spare vehicle'.

Association of Professional Ambulance Personnel spokesman Jonathan Fox said he expected a 'massive shortfall' in the reliability of the vehicles the trust said it cannot afford to replace this year.

'One of the justifications for replacing the trusts was that it was going to have a positive impact on patient care. If you have a shortfall of finances then that premise is going to be seen as hollow.'

In its board papers, the trust admitted the 35 new vehicles were 'significantly less than the number that would ideally be needed to bring the fleet age profile up to an acceptable level'.

It would take several years to address the 'long-standing deficiencies in the fleet', it said. Replacing 50 vehicles would cost£5.6m. All ambulances will be replaced in six years.

A report to the trust's board in June said vehicle replacement schemes varied across the four predecessor trusts but it admitted there had been 'slippage' in the programme since the merger.

It said vehicles not replaced this year and 45 which will need replacing next year mean 138 vehicles will have to be bought in 2008-09, but it did not say whether that would be affordable.

North West Ambulance Service trust was unable to comment.

The reconfiguration of ambulance trusts was announced in June 2005 by the DoH in Taking Healthcare to the Patient: transforming NHS ambulance services.

A DoH spokeswoman said: 'The reconfiguration was about establishing trusts of a size that can deliver appropriate investment in people and resources to underpin current and future services, and ensuring resources are targeted at where they are most needed - improving patient care and supporting frontline services.'