A mothballed former steelworks site in Redcar has secured £71m of government funding as Boris Johnson seeks to cement his support in the former Labour strongholds he won in December’s general election.

The sprawling site, once home to the SSI steelworks that went into liquidation in 2015, has been granted the money to turn it into a business park with an aim to create up to 20,000 skilled jobs by 2040.

Redcar, a coastal town in north-east England, was one of more than two dozen “red wall” seats where Labour voters ditched lifelong political allegiances to back the Conservatives last month.

The prime minister pledged to repay the trust of former Labour voters on a visit to the neighbouring constituency of Sedgefield the day after the election result, with the £71m for SSI one of the first significant cash investments in the region since the poll.

Ben Houchen, the Conservative mayor for Tees Valley, told the Guardian last month that Treasury ministers had planned to announce the funding in the November budget until it was jettisoned by the snap election.

More than 2,200 people lost their jobs when the Thailand-based Sahaviriya Steel Industries (SSI) went into liquidation with its UK subsidiary running up £500m worth of debts. The closure had a devastating effect on the town and neighbouring areas along the River Tees.

The 4,500-acre site has been managed by the South Tees Development Corporation since August 2017 but has been largely mothballed amid a dispute with three Thai banks about the sale of the site back to Teesside. The Treasury said the £71m would be used to pay for the demolishing of old buildings and preparing the ground for the area to be turned into a business park.

Houchen said the public investment would accelerate the ability to target interest from businesses. “I have always said I would be the first to ask government for more money when we needed it for the redevelopment of the former Redcar steelworks site,” he said.

“So, after asking, I’m pleased we will be receiving the £71m to help secure the site and accelerate its preparation for private sector investment. This is another significant step to help us breathe new life into an area that was devastated following the closure of the steelworks in 2015.”

Rishi Sunak, the chief secretary to the Treasury, is due to visit the site on Friday. He said the government backed Teesside’s ambitions to be “a global trading centre with great jobs for world-leading industries”, adding: “We want to unleash the potential in Teesside and across the country to make the most of the opportunities available for the future.”

Houchen said last month that central government had injected £137m into the site since 2017 but that at least another £50m was required before compulsory purchase proceedings to strip the land from the Thai banks in February.

• This article was amended on 13 January 2020 to clarify that it was 14 December, not 13 December, on which Boris Johnson visited Sedgefield.