The scrutiny committee of West Oxfordshire District Council has passed a vote of no confidence in the ambulance service.
It learned that, for category A emergency call-outs, where an ambulance should at the scene in eight minutes, the success rate in west Oxfordshire in February was 41.2 per cent, compared to a government target of 75 per cent.
In April last year the service managed 72.4 per cent. Committee chairman Peter Handley said: "We're on a downward spiral. It's appalling.
"The rural areas are losing out. The service conceded that there had been a "significant drop" in response times, but said they were taking on more staff.
Oxfordshire's ambulance service was merged into the South Central Service in 2006, which also includes Berkshire, Buckinghamshire, Hampshire and the Isle of Wight, with calls routed through Milton Keynes.
In February, there was an hour's delay in treatment when an ambulance called to treat an unconscious 14-year-old girl in a skate park in Grove, near Wantage, was sent to a skate park at Grove in Bedfordshire.
Ambulance service spokesman Alison Brumfitt said: "In February there was a significant drop, but it is not a steady decline.
"Rural areas like west Oxfordshire, unlike the urban ones we cover, are more difficult to get to by ambulance."
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