A Conservative minister in the Foreign and Commonwealth Office used an official visit to Azerbaijan to promote the interests of a billionaire party donor.

Leo Docherty, the Tory MP for Aldershot until 30 May, visited a showroom for JCB machinery in February 2023 and climbed behind the wheel of one the company’s diggers to “help promote UK products in Azerbaijan”. He later posted a photo on X of the visit, tagging the company’s official account.

A Conservative former cabinet ­minister who took donations from the billionaire boss of the JCB digger dynasty – including a £7,000 trip on his VIP private helicopter – oversaw decisions to award his family’s business empire millions in taxpayer-funded green energy grants.

Claire Coutinho also posed for ­pictures promoting Lord Bamford’s personal £100m hydrogen engine project and accepted a £7,500 donation from JCB to her local election campaign while she was the energy secretary in Rishi Sunak’s government.

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JCB has reported an increase in profits last year as strong US sales made up for its exports to Russia ending and faltering demand in the UK and Germany.

The company, one of the largest manufacturers in Britain, said that pre-tax profits rose 44% to £806m last year, up from £558m in 2022, according to a summary of its accounts published on Monday.

JCB, one of the UK’s biggest manufacturers, is investigating a spate of drug use among workers based at its headquarters and has sacked a “significant” number of staff, the Guardian can reveal.

A message sent to UK employees last week by the digger-maker’s group human resources director, Max Jeffery, seen by the Guardian, said it had been conducting a “series of investigations into substance misuse” over the past two months. This had resulted in a “small but significant number of people leaving JCB”.

The influential Tory donors behind the JCB digger empire could be hit with a bill for more than £500m to settle a longrunning investigation by HM Revenue and Customs, the Guardian can reveal.

The investigation into Anthony Bamford, a Tory peer, and his brother Mark, the director of a subsidiary of the Conservative party, is understood to span a complex network of offshore tax havens and companies.

Boris Johnson has accepted another £10,000 of accommodation from the Bamford family, taking their contributions to his lifestyle to almost £50,000 since he resigned as Conservative leader.

The former prime minister registered the additional gift from Lady Carole Bamford, for “concessionary use of accommodation for me and my family in October”.

Boris Johnson accepted free accommodation worth £10,000 from the wife of the leading Tory donor who hosted his wedding party this summer, it has emerged.

The updated register of MPs’ interests shows that the former prime minister accepted a £10,000 gift from Lady Carole Bamford, for “concessionary use of accommodation for me and my family in September”.

Boris Johnson’s attempt to use his India visit to hail the success of JCB, the digger firm owned by a Tory donor, was met with a backlash on Thursday over the use of its machinery in the mass demolition of homes.

The prime minister arrived in India as a fierce row rages in Delhi over the demolition of mainly Muslim settlements in an area of the capital hit by communal violence – an issue that is being considered by India’s supreme court.

• Industrial scion with big money in green energy

The heir to the JCB digger empire, whose father Lord Bamford is one of Boris Johnson’s biggest financial backers, is locked in a legal battle with a former close friend that has shed fresh light on alleged tensions inside one of the UK’s most powerful industrial families.

The case has also raised questions over the conduct of Jo Bamford, a 43-year-old self-styled “green entrepreneur” who is a director at a key JCB holding company and has now set himself up as an investor in bus manufacturing and hydrogen.

JCB, the British tractor firm, has been found by a UK government watchdog to have failed to carry out due diligence human rights checks over the potential use of its equipment to demolish homes in the occupied Palestinian territories (OPT).

The watchdog ruled: “It is unfortunate that JCB, which is a leading British manufacturer of world-class products, did not take any steps to conduct human rights due diligence of any kind despite being aware of alleged adverse human rights impacts and that its products are potentially contributing to those impacts.”

JCB is rightly under close scrutiny (JCB challenged over machinery used to demolish Palestinian homes, 12 October).

You highlight JCB’s donations to the Conservative party. But JCB also donates to a leading children’s charity, the NSPCC, effectively sanitising the company’s reputation.

The British heavy machinery firm JCB’s sale of equipment used in the destruction of Palestinian villages in the Israeli-occupied West Bank is being examined by a UK government body to determine whether its due diligence process complies with human rights guidelines set by the Organisation for Economic Co-operation and Development.

The case is likely to test the degree to which multinationals are responsible if their export goods are sold by local distributors in ways that infringe human rights.