Westcountry towns will "quickly descend into chaos" if plans to let shoppers park on double yellow lines go ahead, it is claimed.
Communities Secretary Eric Pickles says he wants to revive high streets by giving motorists a grace period for parking of up to 15 minutes.
Under the Conservative plans to encourage more trade into struggling town centres, parking attendants would not issue fines to anyone nipping into a shop or leaving their car for up to quarter of an hour but would face fines of up to £130 for dangerous parking.
Councils who would need to enforce the new relaxed rules in Devon and Cornwall have branded the proposals "dangerous", likely to provoke disputes and open to widespread abuse.
Tony Powell, former mayor of Liskeard, who helped form a task force to stop car parking charges damaging trade, said he was "gobsmacked" by the idea.
He added: "We have just been through two years of putting double yellow lines because parking on some roads was causing horrendous problems during the day.
"If everyone was allowed to park on them we would quickly descend into complete chaos – we would need twice as many traffic wardens to regulate it. It is not sensible or well thought out – no-one would use car parks – the Government should instead subsidise free parking."
Mr Pickles believes parking fines are doled out too eagerly, and are partly responsible for killing off the high street, forcing consumers to use out-of-town supermarkets.
But the issue of easing restrictions has caused friction with Coalition partners the Liberal Democrats.
Norman Baker, the Lib Dem transport minister, had been pushing for higher fines and charges to persuade more people to ditch the car in favour of public transport.
Mr Baker said having cars parked for a "very long period" of time on a double- yellow line undermines its purpose and is "unworkable".
Edmund King, president of the AA, said a "thorough review" of the lines would be more effective, perhaps forcing local authorities to ditch one old yellow line for each new one approved.
"Many double lines are there for historical reasons and could be lifted," he added.
"There is plenty of opportunity to ease back on the signs and lines in many places, giving drivers short-term waiting bays instead, so they can stop briefly to buy a paper or loaf of bread."
Local authorities in the region, however, have not welcomed the idea.
Alex Folkes, Cornwall Council's cabinet member for finance and resources, said the lines were "in place for a reason".
"Allowing motorists a grace period to park for a short period of time could cause danger and inconvenience to pedestrians and other road users, making it harder for people to cross the road and increasing congestion as motorists look for places to park," he added.
"There are many reasons why trade has fallen in many high streets over recent years, but we believe one of the ways to improve the vitality of town centres is to encourage people to stay for longer.
In a number of towns, the Council, in conjunction with local members, has introduced a lower two-hour parking charge to encourage longer stays."
Devon County Council said it would "increase the risk of accidents" and be "difficult to enforce", with wardens needing to "wait around".
East Devon District Council said " disputes" could possibly make enforcement "more challenging."
