The reassurance follows reports that dozens of road schemes throughout the UK could be scrapped or delayed because of escalating costs.

Projects thought likely to be affected include a long-awaited revamp of Testo's roundabout scheme in Boldon Colliery.

However, the Highways Agency has denied suggestions it has gone hugely over budget, and it insists the Testo's preferred plan, for a new flyover across the roundabout, is still very much on schedule.

An agency spokesman said: "Public consultation on the A19-A184 Testo's junction improvement scheme began in March this year, with three options under consideration.

"We expect ministers to announce the preferred route in March next year.

"Subject to confirmation of funding, the scheme is expected to start on site in 2012-13 and be completed in 2014/15."

It is hoped the Testo's development will improve traffic flows along the A19 corridor.

The flyover plan follows demands for improvements to junctions to make the most of the £260m New Tyne Crossing scheme.

Figures obtained under the 2000 Freedom of Information Act suggested that several new road schemes across the country have cost three times more than originally estimated.

That sparked fears the total cost of the agency's 56 major schemes could rise from £8.46bn to £12.3bn.

However, the spokesman added: "To say our road-building programme is significantly over budget is wrong.

"There have been no significant changes in out-run costs on schemes open to traffic or schemes in construction since the latest costs were published in July 2008.

"We are progressing the schemes in the national programme as per timetable."

In January, the Government announced an investment programme of up to £6bn over the next six years to improve the national road network.