A Conservative cabinet minister intervened on behalf of one of the world's richest cocoa dealers to get a ban on trading lifted after receiving £40,000 in donations from the millionaire's company to his parliamentary office.

Andrew Mitchell, the international development secretary, reportedly made the intervention after he was asked for help by Anthony Ward, whose firm, Armajaro Holdings, had been banned from trading following allegations that a contractor was involved in smuggling cocoa out of Ghana.

The minister telephoned the British high commissioner in Ghana on the issue, according to internal government documents cited by the Sunday Times, despite the fact it involved British business interests overseas, which is outside Mitchell's remit. Officials in Mitchell's office also contacted the Foreign Office to say that the matter required "urgent attention".

Henry Bellingham, a Foreign Office minister, subsequently lobbied Ghana's vice-president on behalf of Armajaro Holdings. A partial trading ban imposed on the company has now been lifted, although it remains in place in one district of Ghana.

Armajaro provided donations totalling £40,000 to Mitchell's parliamentary office between August 2006 and December 2009. The firm donated £50,000 separately to the Conservative party in 2004.

The Sunday Times said that Ward asked Mitchell to lobby the Ghanian government "at a presidential level" weeks after May's general election. Documents released under the Freedom of Information Act indicated that Foreign Office civil servants raised questions as to why the British government should intervene on behalf of Armajaro. "Is this… something we should lobby on? Or should the UK company realise they have broken the rules and have to pay the price?" asked on official during a recorded exchange of correspondence.

Last night a spokesman for the Foreign Office said: "All representations made by the government in this case were entirely proper and consistent with our support for legitimate British businesses abroad.

"Ministers regularly lobby in support of specific British companies facing restrictions on trade."

A spokesman for Mitchell denied that there had been any wrongdoing. He said: "The letter from Armajaro was dealt with in accordance with normal ministerial procedures."

Paul Farrelly, the Labour MP for Newcastle-under-Lyme, said it was "naive at best" for Mitchell to have become personally involved in the case. "There will always be accusations that, through political donations or contributions to a minister's office, influence is being sought or bought."

The ministerial code states: "Ministers must ensure that no conflict arises, or could reasonably be perceived to arise, between their public duties and their private interests, financial or otherwise."

Ward made headlines in July when he made a huge bet on cocoa through his Armajaro Holdings hedge fund, buying £650m worth.

The deal, the single largest of its kind in 14 years, earned Ward the nickname "Chocfinger". His wealth is estimated at £36m.