County councillors have called on the government to offer assurances that there will be investment in improving key link roads if a third Thames crossing at Gravesham is built.

Kent County Council transport chiefs say they are also concerned the time table for building the crossing means it will not open until 2025.

The issue of whether the council should support so-called Option C as the location was discussed by a cross-party committee, which heard from campaigners who are against the location and say it will lead to irreversible damage to the environment.

Bob Lane, who started a petition against the plan, told the committee: “It will cause immense damage and irreversible harm to the last remaining Green Belt between the urban riverside areas stretching from London to Gravesend and the Medway towns.”

The route would damage the Kent Downs Area of Outstanding Natural Beauty and destroy nearby woods that were a site of special scientific interest, he added.

Residents in the area faced noise and pollution and the crossing would not address any of the issues that faced Dartford, he said.

The new crossing would only reduce traffic levels on the supporting roads by 14%.

“Highways England has deliberately talked up the difficulties and costs of Dartford solution by proposing to demolish businesses and properties and saying it would take six years to widen the A282. This is only a 20th century solution to a 21st century problem.”

There was also criticism from local county councillor Bryan Sweetland, who resigned from KCC’s cabinet because of his opposition to the scheme.

He accused Highways England of a skewed consultation, saying it was the most biased he had ever come across.

“There are too many loose ends in Highways England’s proposals. Will it work? I don’t think so.”

The failure to provide a commitment to improve connecting roads to take the extra traffic coming through Kent was a major concern, he added.

“KCC is signing a black cheque and that is the reason more work needs to be done. This is one of the most biased local consultations I have ever seen,” he said.

But there was support for the council’s backing for Option C.

Cllr David Brazier (Con), who represents Sevenoaks North East, said he understood residents’ concerns but the third crossing was needed for the country as a whole.

“The greater good should prevail...the route is needed - it is about the wider UK interests,” he said.

He likened the scheme to the channel tunnel and the link through Kent, saying there was similar opposition from residents.

“There has to be a third crossing and it has to be at Gravesham East.”

KCC’s cabinet member for transport Matthew Balfour said he had “enormous sympathy for those affected by the route.”

“We must look at ensuring there is proper compensation for those affected. [But] we must appreciate that this is a national problem. For those who live there, it will be a nightmare but for others there is a different agenda.”

Green county councillor Martin Whybrow said the government was being short-sighted.

“Does anyone think this is sustainable? Rather than destroying more and more Kent, we should look at alternatives. We should focus on ports other than Dover and we should be looking at carrying less freight by road and more by freight.”

The final decision on KCC’s view of the crossing option will be taken by the authority’s cabinet shortly.