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.

JCB is owned by the former Tory peer Lord Bamford, whose family is one of the wealthiest in Britain, with an estimated worth of £7.65bn. The Bamfords and their companies have given at least £10.2m to the Conservatives since 2001, including £300,000 so far in 2024 alone.

Last week, the Observer revealed that another Conservative ex-minister, Claire Coutinho, accepted a £7,500 donation from JCB to her local Conservative association while in post as energy secretary in Rishi Sunak’s government.

Coutinho, the MP for East Surrey, also met Bamford and organisations linked to him before and after key decisions that saw companies in his family’s business empire granted millions in government green energy grants. During one trip she posed for photos in a JCB hard hat and hi-vis vest and appeared in a press release describing the company as “brilliant” and “inspiring”. Since leaving government she has flown in JCB’s private helicopter.

Critics said the details of Docherty’s activities in Azerbaijan, together with the donations to Coutinho, gave the impression that major political donors were given special treatment.

At the time of Docherty’s visit, JCB was hoping to double its sales in Azerbaijan, according to a Foreign Office briefing obtained by the newsletter Democracy for Sale and seen by the Observer. “They consistently look for opportunities to raise their profile in Azerbaijan,” it said.

The briefing, released under freedom of information laws, added that Docherty’s “drop-in to the new JCB showroom” in Baku, run by an independent dealer, would “provide an opportunity to help promote UK products”. “There will be a site tour, a demonstration of the machinery, and a chance to drive one of the vehicles. You will deliver a few recorded remarks,” it said.

Sue Hawley, executive director of the campaign group Spotlight on Corruption, said: “The risks of real or perceived conflicts of interest will always arise when party donors get government contracts, grants or trade support.”

JCB said it was a leading UK manufacturer and sold its products overseas through a network of independent dealers, whose role was to maximise sales. Asked about Docherty’s showroom visit, a spokesperson said that if the British embassy or high commission in any territory wished to “use a JCB dealership as an example of a success story based on exports of British goods”, that was a matter for them.

The spokesperson added that JCB welcomed politicians from “all political parties” – it had a meeting with Rachel Reeves in 2022, when she was shadow chancellor – and that leaders were encouraged to meet MPs so they could teach them about JCB and learn about the political world in return.

Last week it was revealed that the company paid for an £8,400 helicopter trip for the Reform UK leader, Nigel Farage, on 25 October to tour a JCB site and meet “senior managers”. A spokesperson for Farage told the Guardian: “Nigel and Lord Bamford are friends.”

JCB and the Bamford family have been regular donors to the Conservatives for two decades. Lord Bamford is friends with the ex-prime minister Boris Johnson, reportedly letting him stay at his properties in Knightsbridge and the Cotswolds and paying £23,853 towards food and flowers for his wedding party.

Several companies linked to the family have received government funding under the Conservatives. In December 2023, a project by Hygen – a company owned by Bamford’s son Jo – was one of 11 granted a slice of £90m in government grants from the Net Zero Hydrogen Fund. Another firm controlled by the younger Bamford, Wrightbus, also won two deals worth £75m in finance from UK Export Finance to export hydrogen-powered buses abroad. There is no suggestion that the grants to Bamford family companies were awarded improperly or that correct processes were not followed.

Since the revelations about JCB’s donation to Coutinho, Labour has written to the shadow energy secretary demanding an explanation about government funding given when she was in post. “The British public will be concerned that such donations may have influenced decisions taken while you were secretary of state,” Polly Billington, Labour MP for East Thanet, wrote. “The public may also be concerned to learn about the donations by JCB given the positive media coverage you appear to have given them.”

Coutinho is yet to publicly respond. Docherty, who is no longer an MP, did not respond to requests for comment last week.

A Conservative party spokesperson said: “All reportable donations are transparently declared to the Electoral Commission. Donations were never a material consideration in government decisions.”