Sunderland Volunteer Life Brigade uses its Land Rover to carry out vital duties along the city's coastline, including search and rescue missions and transporting casualties.

But bosses at the DVLA have refused a string of requests for the makeshift ambulance to be exempt from road tax.

Now the brigade could be forced to slash its patrols because its vehicle excise duty (VED) is to double to £400 a year, as part of measures in Gordon Brown's Budget to clamp down on "gas-guzzlers".

Rose Roberts, company secretary at the brigade, said: "It's going to be quite a blow for us as a voluntarily funded organisation.

"Our only guaranteed income is a grant of £250 from the Coastguard Agency of the Department of Transport. It cost £30,000 to run the brigade last year."

Rose, 63, a part-time civil servant who has worked as a volunteer at the brigade for 14 years, added: "We've applied for an exemption, but we've hit a brick wall. We have been told we do not satisfy the requirements for the exemption category. But I know of mountain rescue teams which do basically the same work as us and they don't have to pay any car tax."

Rose says she was told by workers at the DVLA in Gosforth, Newcastle, that the Land Rover was not eligible for exemption because it does not tow a boat to launch lifeboats and it does not always carry casualties to hospital.

Her husband, Fred, a retired shipyard worker and senior captain of the life brigade, said: "We do a range of rescue services which involve the Land Rover, but the increase in tax may mean I could have to cut patrols.

"We currently carry out patrols every weekend but we may have to cut back."

Fred, 67, a volunteer at the brigade for 35 years, added: "We carry all our equipment on the back of the Land Rover – safety harnesses, ropes, winches, life jackets. It's a vital part of our operation."

Rose said: "We already spend £800 on insurance for the Land Rover. Insurance is our biggest yearly outlay. And with diesel prices going up as well, it's a real problem."

A spokesman for the DVLA said that vehicle excise duty exemptions have a very tight qualifying criteria.

He said: "There is no specific exemption for vehicles that are used for coastal search and cliff rescue. This means that vehicles used for those purposes would be liable to pay the normal rate of VED.

"Decisions on VED, whether structure, rates or alternatives, are ultimately for the Chancellor of the Exchequer. I suggest that the Sunderland Volunteer Life Brigade contact him direct or through their Member of Parliament."

The brigade celebrated its 130th anniversary last weekend. It has saved 800 lives to date.

A spokeswoman for the Humber Maritime Rescue Sub-Centre said "The volunteer life brigades assist us greatly in the work that we do, and we use them as much as we can for searches and rescue missions."