Revealed: The London multi-millionaire bankrolling Caroline Lucas's campaign

A London-based multi-millionaire - whose father is one of the country's wealthiest financiers '“ is bankrolling Caroline Lucas in her campaign to secure a second term as Green MP for Brighton Pavilion, Brighton and Hove Independent can reveal.

James Arbib, 42, has given £20,000 to Ms Lucas and the Green Party - even though he has previously supported Zac Goldsmith, the Conservative MP with a record of supporting environmental causes. And despite the fact that his father, Sir Martyn Arbib, has given nearly £500,000 to the Conservative Party.

Mr Arbib, a Cambridge graduate who is a former investment analyst in the City, is a substantial investor in resource-efficient technologies. He came to wider public attention when it was reported he sold his Chelsea mansion to Hugh Grant and Jemima Khan for £18 million in 2006.

Sir Martyn was knighted in 2003, two years after he sold his Perpetual fund management company for more than £1 billion, receiving £113 million in cash and shares worth an estimated £300 million.

Members of the Arbib family - through the Arbib Foundation - have been heavily involved, since the outset, in Langley Academy, Slough, which opened under Tony Blair's government in 2008.

For his part, Mr Arbib runs Tellus Mater Foundation, a grant-making charity whose mission is "to catalyze a shift to sustainable capitalism: to change the operating rules for capitalism so that finance can better fulfill it's role in directing the flows of Financial Capital to production systems that preserve and enhance Natural Capital".

According to the Electoral Commission, Mr Arbib gave £10,000 to Caroline Lucas on April 8, the same day as he gave £10,000 to the Green Party nationally.

Commission records also show a £2,500 donation by Betterworld Ltd, a vehicle for Henry Tinsley, former chair of Green and Black's, the organic chocolate company.

Betterworld has given more than £100,000 to Labour and the Liberal Democrats to help fight Conservatives in marginal seats; Mr Tinsley  is also involved in 38 Degrees, the online campaigning organisation.

A further £6,000 has been given by Martin Bevis Gillett, 72, after a 1,000-mile sponsored cycle ride in memory of his brother, David, a Green Party activist who died in a cycling accident in 2004.

Penny Kemp, the Green Party's external communications coordinator, said donations were accepted in line with an ethical donations policy that went beyond anything required by law.

She said: "We also make clear that donations are accepted without there being any direct return benefit to the donor. An important factor for us is the track record of the donor and if they are seen broadly to back the same progressive values we promote.

"Mr Arbib has worked for many years to support important projects in the environmental field; for example his foundation has funded some pioneering work on climate change and the economic system. We're grateful to him for supporting Caroline and the Green Party and for his emphasising the importance of keeping a Green voice in Parliament."

Mr Arbib said: 'I think it's very important for the Green Party to have a voice in parliament. I support the work that Caroline Lucas has done to date and want to see it continue in the next parliamentary term. Without a Green voice in parliament, it would be harder to get support across society for the changes that need to happen to move us into a more sustainable and environmentally stable society.'