Calls for a blanket 20mph speed limit for Suffolk's residential roads have been rejected amid opinions that it could not be enforced.

The Liberal Democrat, Green and Independent group put forward the motion to Suffolk County Council's full council meeting on Thursday afternoon calling for a mandatory 20mph speed limit for the residential streets in the county's town and villages, with 30mph only in exceptional circumstances.

The group said it would improve road and pedestrian safety, reduce the air pollution levels and encourage more people to take to their bicycle or walking.

But the motion was rejected by 48 votes against to 20 votes in favour.

Conservative cabinet member for highways Andrew Reid said: "We all want to see speeding on our roads reduced but it is a matter of how best to achieve that.

"Does a blanket, signs-only 20mph speed limit do that? I would contend not.

"Are there measures to improve the current adherence to motorists? I firmly believe there are, and this can be achieved by working on solutions with the government and other agencies such as the police.

"But a one-size-fits-all 20mph limit merely introduces a new layer of rules based impositions."

Cabinet member for the environment Richard Rout said that only using signs would not enable 20mph speed limits to be enforced, where 20mph zones in targeted areas could be because they featured other road changes such as speed cameras, speed humps or chicanes to achieve that.

Councillor Robert Lindsay, transport spokesman for the Liberal Democrat, Green and Independent group who put forward the motion, said that work with the council highways team had identified the cost would be around £4million to implement a signs-only 20mph limit – the equivalent of the council's budget surplus last year, and enforcement would be no more difficult than it is now with 30mph limits.

He said: "In the four years to 2019 there were over 150 people killed in crashes on Suffolk roads and over 1,200 people in Suffolk were seriously injured.

"The majority of these were clustered around towns and villages – that is 40mph roads or less."

Mr Lindsay said it would reduce the number of fatalities, reduce air pollution from accelerating and braking, and encourage a shift to people using bicycles and walking.

He added: "We are the highways authority and it's up to us to change the culture here and the only way we do that is by a blanket 20mph, not by a piecemeal approach."

Green councillor Andrew Stringer pointed to data for Occold village which has had 20mph for more than 20 years, where speeds were on average 7mph less, as a reason to consider backing the motion.