“That’s the last thing I wanted to see,” he told The Times as he peered past a detective at the trademark of HSBC.

In his first interview since being arrested three weeks ago, Mr Brown said that he wanted to get matters resolved quickly. “This dispute is just a disagreement between a bank, the investors and me,” he said.

Mr Brown, whose trademark ponytail has been cut off, took an easyJet flight as he was extradited from Spain. His own $4 million, six-passenger, light business jet was impounded at Biggin Hill. The total price of the easyJet tickets — three returns and a single — was £500. He was expected to spend the night at Bishopsgate police station before being brought before magistrates today. Mr Brown, who was arrested at his villa on Majorca during his 40th birthday celebrations, accepted extradition because he is keen to return to “face the music”. He strongly denies fraud.

Wearing an orange jumper, white shirt and gold-rimmed spectacles, he said that he had nothing to eat during the two-hour journey. He appeared chipper, positive and confident as he chatted animatedly with the detectives either side of him on the flight.

Speaking of his arrest, he said: “It was going to be a special day for me because I was supposed to be celebrating my 40th birthday with my wife and two friends. I don’t (usually) celebrate my birthday because it’s the day after my father died.”

Mr Brown faces 51 allegations in a criminal prosecution launched by HSBC, which accuses him of forging documents involving purported trading of $1 million on financial markets. The bank has also launched a civil action, temporarily freezing his worldwide assets, after it is said to have become suspicious during an internal audit.

City of London Police also want to question him over allegations that he lied to get a new passport by claiming his own had been destroyed in a washing machine in Spain.

The extradition of the Glasgow-born trader comes as the investigation widens into alleged money-laundering involving 5th Avenue Partners Ltd, which he owns. Mr Brown was banned by law from making political donations as an individual because he is not on the British electoral roll. The Lib Dems instead received his £2.4 million donation in a corporate gift from his London investment company.

HSBC has discovered that the money emanated from overseas investors, who have demanded that the Lib Dems return their cash. They have written to the Financial Services Authority demanding that HSBC be banned from banking for failure to manage their funds.

“Unknown to the claimants and other investors . . . numerous wire transactions went in and out of the 5th Avenue accounts without even the slightest concern or monitoring of HSBC. Where was the independent FSA money-laundering agent at HSBC during all this time?”, the investors’ formal complaint states.

The FSA has powers to withdraw permission for banks to accept deposits and can impose huge fines.

The Electoral Commission said last night: “Recent developments have meant that more information about (Michael Brown’s) company is becoming available and we are considering it in detail to see (what) significance it may have in relation to the question of permissibility.”

The Liberal Democrats said yesterday: “We are quite certain it is a permissible donation. We believe that we acted in good faith at all times.”

Last night Mr Brown said he had not heard from the Lib Dems since the reversal in his fortunes. “I haven’t heard a thing. If it is deemed to be an ineligible donation then the money should be returned.”

A spokesman for HSBC said: “As HSBC has not yet had a chance to see or study the complaint in question, we are not prepared to comment.”

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