The Conservatives received £50,000 in the dying days of the election campaign from a company linked to a billionaire who is fighting a court battle over allegations of exploiting his domestic staff, Electoral Commission figures show.

Figures published on Monday show Westminster Development Services, a consortium responsible for redeveloping the Old War Office on Whitehall into a Raffles hotel, made the donation to the Tories on July 1.

According to Companies House, Westminster Development Services is up to 50% owned by AMC Project Services, which itself lists Prakash Hinduja, the chairman of the Hinduja Group and one of Britain’s richest men, as its owner.

Some 10 days earlier, on June 21, Hinduja and three members of his family had been handed prison sentences after they were convicted by a Swiss court of exploiting domestic workers at their mansion in Geneva.

Hinduja and his wife Kamal received sentences of four years and six months, while their son Ajay and his wife Namrata were each sentenced to four years. None of the four were in court.

The court said the four were guilty of exploiting workers and providing unauthorised employment, but dismissed more serious charges of human trafficking.

The defendants deny all of the allegations and are appealing against the verdict, which the family’s lawyers said meant under Swiss law the sentences are without effect and are unenforceable.

A Conservative Party spokesperson said: “Donations to the Conservative Party are properly and transparently declared to the Electoral Commission, openly published by them, and comply fully with the law.”

Monday’s Electoral Commission figures confirmed the Conservatives struggled to raise funds throughout the election, receiving only £225,587 in the last week of the campaign.

In total, the party received just £1.8 million in private donations, around a fifth of the £9.5 million raised by Labour as it secured its commanding majority.

In the last week of the campaign, Labour raised £465,600, including a £250,000 donation from former professional poker player Derek Webb.

Mr Webb, now a proponent of tighter gambling regulations, had previously donated £550,000 to the party under Sir Keir Starmer’s leadership.

Labour also received £100,000 donations from both the GMB trade union and the Fire Brigades Union in the last week of the campaign.

The Liberal Democrats managed to raise £1.7 million over the course of the campaign, boosted by a £100,000 donation in the final week from food business GADF Holdings.

Reform UK raised a total of £1.6 million over the campaign, including £45,000 in the final week thanks in part to a £20,000 donation from businesswoman Margaret Hepburn, who lives in Monaco.

Political parties are required to provide weekly reports of donations of more than £11,180, after the Government increased the threshold from £7,500 in January.

Parties still have 30 days after receiving a donation to check that it is from a permissible source and decide whether to accept it.

The Hinduja family’s legal counsel said in a statement: “Our clients the Hinduja family have been acquitted of all human trafficking charges.

“The family denies all other charges against them. As the family are appealing the case, the previous judgment is not final or binding and the higher court will rehear the case in its entirety.

“Under the Swiss Code of Criminal Procedure, the presumption of innocence applies until a final judgment by the highest adjudicating authority, which has not yet taken place.

“Contrary to some media reports, no members of the family are imprisoned as a result of the verdict. The complainants in this case have withdrawn their civil complaints against the family.

“The family has full faith in the judicial process and remains confident that the truth will prevail.”