Image copyright Michael Brown Image caption Michael Campbell-Brown now works for the outsourcing company Serco

A convicted businessman who donated £2.4m to the Liberal Democrats has said it was the "stupidest" thing he has ever done in his life.

Michael Brown made the payment - a record sum for the party - in 2005.

But a year later, he was jailed for perjury and then fled the UK for the Caribbean while facing other criminal charges.

He told BBC News he now regrets the donation because it led to an "onslaught of recognition".

"I feel bad because giving the money brought me to the forefront... and caused an enormous amount of pain on my family," he said.

"I broke the law and deserve the pain that I got - my family never deserved that."

In a wide-ranging interview - his first for 12 years - Michael Brown, now known as Michael Campbell-Brown, revealed he is using his experience of being a prisoner to help other inmates adapt.

The 53-year-old is employed by outsourcing giant Serco, which runs six prisons in England and Scotland, to improve procedures in the first days after offenders are locked up, when they are most vulnerable and at risk of suicide.

He trains prisoners to be "mentors" so they can advise and guide new arrivals.

"When a prisoner comes off that bus, he's nervous beyond belief and he does not know what is going to happen in the next four or five hours of his life - or the next four or five days," he said.

Media playback is unsupported on your device Media caption Michael Brown was filmed being held in a cell in the Dominican Republic

During his first spell behind bars, which lasted 12 months, the Glasgow-born financier said he witnessed prisoners harming themselves and was "absolutely petrified".

Following his release, he faced the prospect of being sent back to jail after he was charged with further offences, relating to the theft of an investment of almost £8m from Martin Edwards, the former Manchester United chairman.

"I'd brought shame on my family, I'd brought stress on my family and I thought, there's two ways I can deal with this - one is to take the final step, the other one is to circle the wagons and get out of Dodge," he said.

'Extravagant lifestyle'

In 2008, while on bail awaiting trial, he took a cab to Gatwick airport and, using a false passport, he flew to the Dominican Republic under the name "Darren Nally".

The Dominican Republic does not have an extradition treaty with Britain.

He remained in the country for four years, during which time he was found guilty in his absence of theft, providing false information and perverting the course of justice.

The court heard he had secretly spent cash from investors on the Lib Dem donation and to fund an "extravagant" lifestyle.

His actions amounted to a "breach of trust", the trial judge declared.

After Campbell-Brown was tracked down, he returned to the UK, where he served half of a seven-and-a-half year prison sentence.

He now admits that he was motivated by a misguided desire to impress people, thinking they would respect him if he was a "larger-than-life character" - and by a craving to be rich.

"My greed got the better of me," he said, adding that he's "horrendously sorry" for what he did to Mr Edwards.

Blogging

After he was let out in 2016, Campbell-Brown began blogging and giving talks about penal issues, and worked at the publicly-run Leicester Prison and in jails run by G4S.

The work stopped for a while last year, after it was reported that the Spanish authorities were investigating him over allegations of money laundering.

He has denied that he's facing any "active" inquiries, and there has been no confirmation that any such investigations are taking place.

Campbell-Brown has since been given clearance to work for Serco and was recently asked to address a conference attended by prison officers, which was organised by the well-respected Butler Trust.

He now deeply regrets the controversial donation that thrust him into the spotlight.

He was an admirer of the Liberal Democrats' then-leader, Charles Kennedy, and wanted to "level" the political playing field with the Conservatives and Labour in the 2005 general election campaign.

But he said the £2.4 million payment, made via his firm, Fifth Avenue Partners Ltd, should have been rejected by the party.

"They should have said to me: 'But Michael, you don't live in the United Kingdom, you're not registered on the voters' roll, your company was only born six months ago; really sorry Michael, thanks for coming, but no thanks,'" he said.

"That's what they should have done, but of course, you know, the pound signs tend to obscure absolutely everything else."

'Good faith'

Although the Lib Dems faced calls to return the donation, they kept it after the Electoral Commission concluded they hadn't broken any rules and had accepted the payment in good faith.

But Campbell-Brown no longer supports the party because of the way he believes Mr Kennedy was forced out as leader in 2006, amid concerns that his drink problem was affecting his job.

He died in 2015, at the age of 55.

"They drove him out... because he was an alcoholic," he said.

"That person then dies an early death. I'm sorry, you're responsible for that," he added.

The Lib Dems are disgusted by that accusation - a source said they would not "dignify" it with a response.

As Campbell-Brown, a self-confessed "Walter Mitty" character, tries to rebuild his reputation, as someone committed to improving the lot of prisoners, he may find it harder than he thinks to shake off his old political connections and criminal past.

Hear more on this story on BBC Radio 4 Broadcasting House this Sunday, and Sunday 25 August.