Rishi Sunak has torn into Welsh Labour for its implementation of 20mph zones, saying they are "holding Wales back".
Speaking at the Welsh Conservative conference in Llandudno, the Prime Minister said: "When you listen to those labour candidates it's painfully apparent that they don't offer anything new - it's just more of the same."
He claimed the the Labour Party is "doing everything to make life more difficult for people".
The PM said: "Yesterday when I was out and about I was really struck by the impact of the policy of 20 mph zones - the day-to-day impact it's having on everyone's lives.
Rishi Sunak has torn into Welsh Labour for its implementation of 20mph zones, saying they are "holding Wales back"
PA
"It just shows how out of touch Labour in Wales are with the needs and concerns people are."
Sunak added: "'I can see why someone who likes making U-turns as much as he does, and has absolutely no plan for where he wants to take the UK, finds the idea of making everyone drive at 20mph and banning all new road building very appealing.
"But the rest of us say 'dim diolch'.
'"All they have succeeded in doing is slowing Wales down by 4mph. And the cost of this to the Welsh economy? £4billion, a billion pounds per mile (per hour)."
The scheme was introduced by the Welsh Labour Government in September, with most residential roads across Wales having their speed limits changed from 30mph to 20mph.
The Welsh Government says the changes were made in order to make streets safer and save lives.
The PM also used his speech to say the public is “feeling that the economy has turned the corner” and “things are getting better”.
The Prime Minister said: “There is a palpable sense out there, regardless of what Keir Starmer might want to say because he’s always keen to talk down Britain, I can tell actually on the ground people are, since the beginning of this year, feeling that the economy has turned the corner.
“They do see those green shoots. They can see that things are getting better.
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“Inflation has been more than halved, mortgage rates starting to come down, wages have been rising for six, seven months in a row now.
“We just saw today … energy bills significantly down. Consumer confidence, business confidence, again, survey out yesterday, highest it’s been in years. Businesses like yours feeling better about the future.
“And that is why it is so important that we stick to our plan.”