'Something needs to happen on the A47', Labour's shadow roads minister has admitted – but he stopped short of matching the prime minister's promise to upgrade the route.

Labour turned on David Cameron last night over his pledge to invest in the A47, claiming it was a 'pre-election con trick' and Richard Burden said his party would have to go through the figures with a 'very fine tooth comb' before a Labour government could say if it would include it in its infrastructure plans.

A political war of words broke out after Great Yarmouth MP Brandon Lewis accused Labour of 'delivering nothing in 13 years'.

But Mr Burden claimed it was the current government that had scrapped plans to upgrade a section of the route between Blofield and North Burlingham when it won power in 2010.

Mr Cameron announced yesterday that the A47 would be upgraded as part of a £15bn road investment – a move hailed by local MPs.

But details of which sections of the route would be upgraded, and when work would start, are not yet clear. More details are expected in the Autumn Statement next month.

Mr Burden said he wanted to 'be straight with people', adding: 'We recognise that something needs to happen on the A47, because there are jobs relying on it, and that part of the country needs that to happen, but we are going to have to go through what the government is saying with a very fine tooth comb to work out what is new money, and what is pretend money, and how we can make more sense of that.'

He said the Labour Party would put an end to 'stop-go funding' by setting up an infrastructure commission to make long term budget decisions and to avoid 'election gimmicks'.

UK Independence Party councillor Toby Coke, who is Norfolk County Council's chairman of the Environment, Development and Transport Committee, welcomed the announcement and said investment into improving the A47 was 'vital'.

But added that 'the devil will be in the detail'.

'We are seeking a real commitment from the government, and anything less than £500m will show that the government is more concerned about funding its commitments overseas than it is funding vital infrastructure projects at home, like the A47.'