UK anti-corruption investigators targeting high-profile world figures have been asked to investigate the finances of a former Mauritian Prime Minister after £4m in cash was discovered at his home.

Ex-premier Navin Ramgoolam – a doctor and British-trained lawyer dubbed “London boy” by his critics – was led from his home in handcuffs in February after the discovery of the cash in a safe, three months after his surprise loss in a general election.

Senior figures from the island’s new government visited Britain in the summer to lobby for a National Crime Agency (NCA) investigation into the 68-year-old British passport holder for alleged corruption in Mauritius. Police in Mauritius are investigating claims that he or his associates secured corrupt money from deals including the purchase of six Airbus aircraft by the national carrier, and received sums from foreigners seeking naturalisation on the Indian Ocean island, according to government sources on the island.

Mr Ramgoolam – whose backers include Conservative MP and QC, Geoffrey Cox – says that he is the victim of a dirty tricks campaign. His supporters claim that political foes have fabricated claims to stop any political comeback by binding him up in damaging prosecutions for years.

The former Prime Minister, a three-time general election winner and leader of his political party for more than two decades, has denied any wrongdoing and said that  the money – which included about half new consecutively numbered US dollar bills – represented campaign funds given by supporters.

“He has given explanations to the police as to the provenance of these funds,” said his Mauritius-based lawyer Gavin Glover. The FBI is investigating the source of the dollar bills.

The NCA is believed to have contacted the island authorities for details of credit cards found in Mr Ramgoolam’s safe that included two Centurion American Express cards given only to high-spenders. Mr Rangoolam, who owns a Rolls-Royce with a personalised number plate in London, has vowed to open his accounts to independent scrutiny in an attempt to persuade the NCA that he owns no property in Britain and only legitimately amassed savings. Banks in the UK shut down his accounts after the arrest in February.

“There are no properties, no share portfolios, no homes or houses [in Britain],” said a source close to Mr Ramgoolam. “All he has got are some savings acquired over many years including as a physician in Britain that amounts to about £150,000 and a car. He will be fully  co-operative and seek to assist any inquiry from the NCA should it come.”

Any British investigation into Mr Ramgoolam would fit the profile of the more than 20 high-profile politicians being targeted by the National Crime Agency’s International Corruption Unit (ICU).

The unit is currently involved in dozens of operations in 20 jurisdictions and about £200m of assets have so far been restrained by officials in the UK and abroad. Britain is one of the key centres of operation for corrupt powerbrokers to launder and invest their millions.

Last week, Nigeria’s former oil minister Diezani Alison-Madueke was arrested in London, according to her family. She is believed to be one of five people – and the first big scalp claimed by the ICU. Though the NCA didn’t disclose any names, the arrests were thought to be part of an investigation into suspected bribery and money laundering. Ms Alison-Madueke was oil minister between 2010 and 2015. She denied wrongdoing when it was alleged that $20bn of oil money had gone missing when she was in office.