Government transport officials have spurned an invitation to explain why the costs of two crucial road improvement schemes along the A21 have soared by more than £111million.

County councillors had asked officials from the Highways Agency to attend a meeting of KCC’s backbench watchdog scrutiny committee on Wednesday to answer questions about the spiralling costs of plans to dual the A21 between Tonbridge and Pembury and a related scheme to improve the road between Kippings Cross and Lamberhurst.

The cost of the scheme between Tonbridge and Pembury has increased from £48million to £112million and it has gone up by £63million to £103million between Kippings Cross and Lamberhurst.

Both are seen as crucial towards unlocking a notorious bottleneck on a key transport route in the south east. However, the soaring costs have triggered fears that they could now be delayed for years or even abandoned altogether.

But the cross-party committee was told the Highways Agency had declined KCC’s invitation. Instead it was left to county road chiefs to field questions about the two projects.

Cllr Keith Ferrin (Con), cabinet member in charge of roads, ruled out the idea of KCC making up some of the shortfall, saying it was unrealistic. He told the committee the rising costs could lead to the cancellation of one, if not both, schemes. He also questioned whether the new Pembury hospital could be built if that happened because of planning conditions that had been imposed to ensure transport connections were improved.

“If these new estimates are correct, I do not see how both can be achieved. We are worried the Highways Agency will not stump up the money and as a result, will compel the Regional Transport Board to take one of these schemes out. If you look at the Government’s record, it does tend to cut things out rather than put up extra money. We are greatly concerned that one or both of these schemes could be abandoned,” he said.

Pressed about what KCC could do, he said: “The only answer is to continue to urge the Government to make sure the money is available.”

Meanwhile, Cllr Roy Bullock, who is also the leader of Tunbridge Wells council, urged KCC to organise an alliance of south east councils who could be affected by any delays. “We need to mobilise all those affected to raise it up the agenda.”

The Highways Agency says the estimated costs have come about as a result of a review of all major road schemes, the so-called Nichols review. In a statement, it said: “These are interim estimates which we have provided to the region to help them decide on their priorities and programming. Nichols recognised that estimating road scheme costs is inherently difficult, and subject to uncertainty and showed that the main reason behind the increases was the higher than expected rate of construction inflation.”