David Cameron meets Rukon Ahmed, 15, in Queen Street, Cardiff

But on his first visit to Wales since becoming leader he said devolution was here to stay and the Tories would offer "constructive opposition".

Mr Cameron said there should be a referendum to decide if the assembly gains more muscle.

Speaking in Cardiff, he also attacked Labour First Minister Rhodri Morgan as an "old-fashioned statist".

Such a left-wing leader David Cameron's description of First Minister Rhodri Morgan

Mr Cameron went on a walkabout in Cardiff's main shopping area, Queen Street, on the day another poll put the Conservatives in front.

The poll, by ICM in The Guardian, put the Tories on 37%, one ahead of Labour, compared with a five-point Labour lead a month ago.

Mr Cameron said it was "perfectly acceptable" for Conservatives in Wales to take a different view to Tory policy in England, such as on university tuition fees.

"My view for England is that universities need to be well funded and we need a strong science base and I think that means that students will have to make a contribution through their education," he said.

Mr Cameron says Tories can get back in touch with Welsh voters

Tories have previously supported a referendum on the future of the assembly, including an option to scrap it.

But Mr Cameron said he believed in devolution and wanted to make it work.

However, next month in the Commons his MPs will vote against the Government of Wales Bill offering more power to the assembly.

'Keeping it real'

Mr Cameron said the bill had both good and bad elements.

It was right to separate the legislative and executive functions of the assembly, he argued, but plans to ban candidates from standing in both constituency seats and on regional lists was "rather a spiteful move to have a go at the Conservative Party".

He said as Mr Morgan was "such a left-wing leader" and an "old-fashioned statist" there was an opportunity for Tories to offer public service improvements and "to get back in touch with the aspirations of the people of Wales".

But Welsh Secretary Peter Hain said: "Despite the Cameron hype about a new beginning on devolution, the Tories have proved they are still wedded to the same old policies.

"Far from wanting to make the assembly work, they haven't moved one inch in their hostility to the assembly."

On Mr Cameron's visit to the shopping centre, a group of track-suited teenagers who gathered to speak to him said they were impressed.

Michael Conceica, 16, of Grangetown, Cardiff, wearing a hooded top and diamond stud earring, said: "I think he's different, he's keeping it real."

Mr Cameron, whose wife Samantha is due to give birth in February, confessed he had yet to do his own Christmas shopping.

"I'm spending all day shopping tomorrow," he said. " I've got to do it all tomorrow or I'll be in trouble."