The Liberal Democrats' biggest donor changed his name before he vanished awaiting a multimillion-pound fraud trial, an investigation by The Times has discovered.

Michael Brown, whose record £2.4 million donation to the party is in jeopardy if he is convicted, is now registered as Michael Campbell-Brown on the electoral roll.

His new name has been used to apply for a bank account and two credit cards. The Times has seen official letters addressed to his double-barrelled name that have been left unopened at the door of his abandoned three-bedroom flat.

His appearance has also altered, according to a neighbour. His dyed strawberry-blond goatee has grown into a full grey beard, in contrast to published photographs of him.

Michael Robert Alexander Brown was due to be tried next month with 18 offences relating to money laundering, theft, perverting the course of justice and other fraud-related matters.

A judge at Southwark Crown Court issued an arrest warrant on Tuesday after a request from City of London Police. Mr Brown had breached his bail conditions. He was required to live at a flat in Hampstead, northwest London, and to report to the local police station three times a week.

If Mr Brown is convicted and it emerges that the company he used to channel money to the Lib Dems never traded in Britain, the party may be forced to surrender the £2.4 million.

The Electoral Commission said yesterday: “We are waiting to see what new evidence comes from the trial, if any. There is the possibility the Liberal Democrats could be asked to pay the donation to the Consolidated Fund [the Government's bank account].”

The earliest evidence that Mr Brown was adopting a new name comes from the electoral roll. He used his name Michael Brown when his local council registered him in August 2007, but in September he returned a document to Camden electoral services stating that his surname should be registered as Campbell-Brown.

The Times yesterday visited Mr Brown's home in a mansion block in a wide tree-lined road near Hampstead Heath, close to the former home of the footballer Thierry Henry. In the shared hallway The Times saw five letters addressed to Michael Campbell-Brown, including post from NatWest bank. He also had a letter from Capital One, the credit card company.

The Times has seen material relating to previous bank accounts in which he used his birth name of Michael Brown rather than the double-barrelled version.

Mr Brown's wife of 15 years is Sharon Campbell. Unlike him, she is free to live at their home in Majorca.

One neighbour said that he last saw the Glasgow-born businessman about three weeks ago. Steven Waters, 47, a wine importer, said that he saw Mr Brown drive up to their shared building in a silver Mercedes before walking briskly to the front door. “He is now wearing a full grey beard, which is different to photographs that I have seen of him where he has a goatee,” he said. “His hair appears to be longer and has gone grey.”

His solicitor, Jamil Ahmud, who has been trying to contact Mr Brown, declined to comment on his client's apparent name change. He added that his client had not changed his appearance in the weeks before he disappeared. “Any suggestion that Mr Brown has altered his appearance to abscond is nonsense,” he said.

A friend of Mr Brown claimed that he had changed his name as a tribute to his wife. “I believe that he has done this because she has been there for him,” he said.

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