In a video filmed shortly before the UK hosted the Cop26 climate conference, Boris Johnson strolls alongside Jo Bamford and his father, the JCB boss, Anthony Bamford. Behind them is a JCB digger, and a big green bus is parked just across from the Houses of Parliament for a photocall. The prime minister quizzes the men about the economics of switching engines from fossil fuel to hydrogen. “It’s the same cost as running it on diesel,” Jo Bamford replies. “It’s already the same.”

The video, posted by Jo Bamford’s gas distribution company, Ryze Hydrogen, on its Instagram feed in October, shows the privileged access the businessman enjoyed while lobbying for hydrogen to take a central place in Britain’s transition from fossil fuels.

The UK government this year said hydrogen, which releases only water when used as an energy source, could make up to 35% of the UK’s energy consumption by 2050 as part of its net zero plans.

Bamford’s eldest son, who bears the same name as his grandfather, the JCB founder, Joseph Cyril Bamford, runs three businesses focused on hydrogen. He came to attention in 2019 by buying Wrightbus, the bankrupt maker of London buses, and plans to supply the capital with new hydrogen doubledeckers with gas provided by Ryze. More recently, he has started a fund that hopes to raise £1bn to invest in hydrogen.

The Bamfords have described their vision of using hydrogen to power diggers, buses, and other parts of the economy – and they have used their political connections to promote that vision.

Lord Bamford is 38th on the UK’s rich list with a net worth of £4.6bn, built up mainly through the family company, according to the Sunday Times. He is one of the big Conservative donors: the Bamfords and JCB have donated £8.7m to the party since 2002, while JCB gave various pro-Brexit groups a cumulative £670,000 before the EU referendum, according to Electoral Commission records.

Jo Bamford, who like his father attended the Catholic boarding school Ampleforth, has himself donated £75,000 to the Conservatives. He also employed the MP and the former Northern Ireland secretary Julian Smith as an adviser until November, paying him £60,000 a year for 20 hours’ work – the equivalent of £3,000 an hour. Smith resigned shortly after the Guardian reported on his external jobs.

It has been reported that the Bamfords have also provided other benefits to the prime minister. As Johnson recovered from Covid during the first lockdown, he received luxury ready meals worth £27,000 from Daylesford Organic, the company founded by Lord Bamford’s wife, Carole, according to the Daily Mail. Johnson has also reportedly used a helicopter and private jet registered to Lord Bamford to travel on official trips and campaign visits, while JCB paid him £10,000 before a speech in January 2019 in which Johnson praised the company, six months before he won the Conservative leadership.

In a 2019 election stunt Johnson drove through a polystyrene wall using a JCB digger with “get Brexit done” emblazoned on its bucket.

Wrightbus has won taxpayer-funded contracts for green transport worth nearly £80m in the past three years. These include a £12m contract from Transport for London (TfL), won before Bamford’s takeover, to build England’s first fleet of hydrogen-powered doubledeckers. In December 2020 it won a £66m contract from Northern Ireland’s government for zero-emission battery and hydrogen buses; it is also providing buses to Aberdeen, Birmingham and Brighton and Hove under various taxpayer-funded schemes.

Beyond the contracts, Wrightbus has said it received £6m in state funding from TfL, £5m from EU bodies, and £1m from the UK government’s Office for Zero Emission Vehicles.

• This article was amended on 22 December 2021. Jo Bamford is the founder and executive chair of Ryze Hydrogen; it is not his father Lord Bamford’s company as an early version said.