Banks and hedge funds are spending millions on the fight over Britain's future in Europe - but it could remain secret

Millions of pounds are pouring into either side of the debate over whether Britain should stay in Europe or leave - but just how much each side is getting and from who could remain largely a secret.

Bloomberg points out in an article on Thursday that both the "Remain" and the "Brexit" (a British exit from Europe) camps have received huge amounts of funding over the last six months in preparation for the June 23 referendum.

But the bulk of cash appears to have come before the February 1 deadline when the Electoral Commission requires all donations above £7,500 to be made public. It means many major corporations and individuals trying to sway public opinion could remain anonymous.

Bloomberg quotes Darren Hughes, deputy head of the Electoral Reform Society, as saying: "We need to know who's giving the money and who's trying to influence the debate. We're concerned about unreported income because the regulated period is too short."

Despite the lack of disclosure requirements prior to February 1, many donations have leaked out. Here's a rundown of the main backers we know about on each side:

Remain

• David Sainsbury: Great grandfather set up supermarket J Sainsbury's. Provided seed funding for Britain Stronger in Europe, according to Bloomberg.
• Goldman Sachs: Backed Britain Stronger in Europe at the end of January. A spokesman told Bloomberg the bank put in £500,000.
• JPMorgan: Also backed Britain Stronger in Europe around the same time as Goldman. Bloomberg says $500,000 donated. Unconfirmed.
• Morgan Stanley: Bloomberg says $500,000 donated. Unconfirmed.
• David Harding: Founder of hedge fund Winton Capital Management is believed to have backed Britain Stronger in Europe in November. Donation was said to be several millions at the time.
• John Armitage: Founder of hedge fund Egerton Capital also reportedly donated to Stronger in Europe around November.

Leave

• Crispin Odey: The founder of hedge fund Odey Asset Management was one of the founding members of the "Vote Leave" campaign and is believed to be a significant backer.
• Peter Cruddas: The former Conservative Party Treasurer and founder of CMC Markets was another founding member of "Vote Leave" and, according to the Financial Times, put £1 million into the group in November as seed funding.
• Sir Michael Hintz: The founder of hedge fund CQS was "considering" a big donation to the Vote Leave campaign in November, according to the Financial Times.

These are just the names that have either leaked publically or been announced so far in the referendum debate - there are likely a lot more big donations going on behind the scenes.

Both groups have strong links to business: the remain campaign is chaired by former Marks & Spencer CEO Sir Stuart Rose, while founding members of the "Vote Leave" group include JML founder John Mills, Phones4U founder John Caudwell, Reebok founder Joe Foster, Numis Securities CEO Oliver Hemsley, and Patisserie Valerie chairman Luke Johnson.

The BBC reported that Vote Leave is planning to spend at least £20 million on the campaign, around half the total the Conservative Party spent in the year leading up to last May's general election. That implies very deep pocketed backers.

The Electoral Commission will chose the official campaign for each side (there are various factions at the moment) in April, after which the designated groups will be required to publish their first spending reports by the end of the month. Electoral Commission spokesman James McGrory declined to tell Bloomberg if groups would disclose donations it received before February 1.