Campaigners fighting plans to build a Lower Thames Crossing where they live have lashed out at the “scandalous” handling of the project’s consultation – which saw the views of 13,000 people lumped together as 14 responses.

The Lower Thames Crossing Association wrote to Transport Secretary Chris Grayling – before he relinquished his job due to the election campaign – describing the “gross misrepresentation” of objections to the plans put forward by Highways England.

Earlier this month, Mr Grayling gave the go-ahead to proposals for a £4.4 billion tunnel east of Gravesend linking motorways in Kent and Essex.

Highways England said the route will carry 78,500 vehicles each day in its opening year and will reduce traffic at the Dartford Crossing by 14%.

However, the scheme was opposed by residents concerned about damage to the countryside and rising traffic levels.

The Lower Thames Crossing Association said Ipsos MORI, the organisation which collated the responses for Highways England, did not show the true level of opposition to the plans because it consolidated 13,284 responses in 14 campaigns.

These were not included in a graph showing public responses to the location with the crossing, which claimed about 14,000 strongly agreed and 11,000 strongly disagreed.

If the 13,284 responses allocated to the campaigns were also included, the total number who disagreed would have grown to more than 25,000.

Lower Thames Crossing Association chairman Bob Lane said: “Ipsos MORI and Highways England have discounted the opinions of over 13,000 people across north Kent and south Essex who opposed the scheme, and lumped them together into just 14 ‘organisations’.

“It is scandalous that the opinions of over 13,000 people whose lives will be devastated by the crossing can be cancelled out by just 14 individuals in favour of the scheme.”

The association pointed to a series of examples which it said supports its claim.

It said the opinions of 946 Shorne residents opposed to the crossing were counted as a single organisation because they used similar wording in their consultation responses.

It claimed another petition which obtained 2,778 signatures is reported to have obtained only 37 signatures.

Mr Lane said the misrepresentation of the figures could have misinformed ministers when making their decision about the crossing. The association called on the Transport Secretary to investigate the report by Highways England.

Mr Lane said: “How can the government be expected to make an informed decision when the information it is given is so badly flawed?”

A Highways England spokesman said: “The announcement of the preferred route follows an exhaustive review of options and extensive analysis of more than 47,000 responses to our 2016 public consultation.

“Of the 47,034 responses received, 13,284 were identified as being associated with an organised campaign, which are identically worded responses.

“We considered each response very carefully and carried out further assessment of the options before making our recommendation to government.

“Overall there was strong and widespread support for a new crossing at Location C, though we acknowledge that there was strong, mainly localised opposition.

“A new crossing at Location C offers the improved journeys, new connections, network reliability and economic benefits that only a new, alternative river crossing, away from Dartford, can provide.”

About 55 million journeys are made on the Dartford Crossing each year. It was designed for 49 million.