A cabinet minister faces a parliamentary inquiry into his links with a cocoa magnate who donated £40,000 to his political office.
Andrew Mitchell, the International Development Secretary, denied any wrongdoing by intervening on behalf of Anthony Ward, a wealthy businessman nicknamed "Chocfinger" who was seeking to get a trade ban lifted.
Sources close to the minister insisted that proper procedures were followed. But a Labour MP last night referred the case to the Commons standards watchdog, claiming the contacts between the two men raised serious questions about the minister's conduct.
Mr Ward's company, Armajaro Holdings, donated £40,000 to Mr Mitchell's parliamentary office between 2006 and 2009 to support his work as shadow International Development Secretary.
As well as the donations to Mr Mitchell, Armajaro gave a £40,000 gift to the Conservative Party in 2004.
With a personal wealth estimated at £36m, Mr Ward is one of the world's richest cocoa traders, having cornered much of the global market.
In Ghana, however, Armajaro was hit by a ban last year on trading in parts of the country following allegations that one of its contractors had been smuggling cocoa.
According to documents obtained by a Sunday newspaper, Mr Ward wrote to Mr Mitchell weeks after the general election asking the new minister to lobby "at a presidential level" against the embargo.
In his letter he protested that the ban was disproportionate and was being felt throughout the company. Mr Mitchell telephoned the British high commissioner in Ghana on the subject, even though it was outside his department's remit. His officials also contacted the Foreign Office to say the ban on Armajaro required "urgent attention".
Henry Bellingham, the Foreign Office Minister, lobbied Ghana's vice-president on behalf of the company. The ban has now been lifted in all but one of the west African nation's districts.
Internal papers released to The Sunday Times under freedom of information laws suggested that civil servants in the Foreign Office queried whether it was appropriate to intervene. One official wrote: "Is this... something we should lobby on? Or should the UK company realise they have broken the rules and have to pay the price?"
A spokesman for the Department for International Development said: "The letter from Armajaro was dealt with in accordance with normal ministerial procedures and it was immediately made clear that the Conservative Party had previously received donations from the company." He added that the matter had been referred to the Foreign Office "through the normal channels".
The department confirmed that Mr Mitchell had spoken to the High Commissioner in Ghana, but stressed he declared his personal interest and said he was only seeking an update on the situation. A record of the conversation was taken by officials.
But John Mann, the Labour MP for Bassetlaw, said: "Reports that Andrew Mitchell lobbied on behalf of 'Chocfinger' raise serious questions about the Secretary of State for International Development's conduct. Was Mr Mitchell acting in the best interests of the British Government or a donor that has subsidised his Parliamentary office and funded the Conservative Party?"
He said he had personally referred Mr Mitchell's case to the Parliamentary Commissioner for Standards to "ensure the British people get answers to these important questions".
Paul Farrelly, the Labour MP for Newcastle-under-Lyme, said Mr Mitchell had been "naïve at best" to become involved in the case.