Regulators would probably welcome just about anyone who offered to take Northern Rock off their hands. Even so, the Bank of England and the Financial Services Authority might have to think twice before allowing Jose Maria Ruiz-Mateos take control of the mortgage lender.

The controversial Spanish entrepreneur has contacted Adam Applegarth, Northern Rock’s chief executive, claiming he is leading a group of Spanish investors who want to buy a controlling stake in the bank.

The move appears to be Mr Ruiz-Mateos’ first attempt to get back into the banking business since 1983, when his industrial and financial holding company, Rumasa, was confiscated by the Spanish government because it was on the verge of collapse.

The seizure of the business, a mish-mash of troubled companies and banks, marked the beginning of an epic 14-year battle with the government. Mr Ruiz-Mateos fled to London, was detained in Frankfurt, extradited to Spain, charged with a host of criminal charges, held under house arrest in Madrid and eventually acquitted in 1997.

At the same time, he mounted a public campaign against the Socialist ministers he accused of persecuting him. In 1989, he punched Miguel Boyer, Spain’s former finance minister. He also found time to win election to the European Parliament, which helped win him immunity from prosecution.

Officials at Nueva Rumasa, Mr Ruiz-Mateos’ new holding company, said they had sent a fax to Northern Rock last Friday inquiring about buying a controlling stake. So far, however, there have not been any talks between the two sides. Northern Rock declined to comment, but people close to the bank said they were not planning any discussions.

It is unclear how Mr Ruiz-Mateos and his unnamed investors plan to finance the deal. “He always wanted to buy a bank. It could be an interesting opportunity,” an aide said. Asked how Mr Ruiz-Mateos planned to fund an estimated £30bn of short-term wholesale financing on Northern Rock’s balance sheet, she replied: “He would expect the support of the Bank of England.”

Mr Ruiz-Mateos has a history of mounting colourful stunts. In 1988 the father of 13 made an offer to buy Spantax, the troubled charter airline. In 1992 he showed up in a Superman outfit at a branch of a local bank to announce his acquisition of Rayo Vallencano, the football club.

In recent years, Mr Ruiz-Mateos has shown an interest in troubled businesses. Nueva Rumasa has bought Clesa, the Spanish subsidiary of Parmalat, the defunct Italian food group, for €188m (£132m). Buying Northern Rock would be much more expensive and even if Mr Ruiz-Mateos could persuade the bank he was serious, it seems a stretch to think that regulators would agree.