PLANS to boycott controversial American-made ambulances could cripple the North-East's 999 service.

Half of the 110-strong fleet used by the North-East Ambulance Service could be taken off the road if a threat by the Unison trade union is carried out.

Boycott plans were drawn up after two wheels fell off a Chevrolet while it was answering a 999 call on Wearside.

The incident last month was the latest in a string of incidents involving Chevrolets.

Trust managers have stressed that the Chevrolets are safe to drive and have stepped up safety checks.

Paramedics are now being balloted by Unison over whether they would be prepared to refuse to take out Chevrolets on safety grounds.

Ray McDermott, Unison branch representative for the the North-East Ambulance Service (NEAS), said: "A consultative ballot has now been sent out to all our members about what action should be taken with regard to them."

The ballot forms ask staff whether they would be prepared to refuse to take out a Chevrolet.

Paramedics are also being asked whether they would be prepared to take industrial action if colleagues were disciplined over a boycott.

A spokeswoman for the NEAS said: "We are working with staff and union representatives to try to resolve these problems. The Chevrolets are as safe as any other vehicle in our fleet and we are putting measures in place to try to reassure staff."

According to the trust the main reason for purchasing Chevrolets in 1993 was for their "superior crash protection".

In a briefing document recently sent out to health authorities, the trust states: "although there have been some reliability issues with these vehicles, their record in terms of crash protection to the occupants of the vehicle is exemplary."

The trust has said it will phase out Chevrolets over the next three years.