One of the Conservative Party's biggest donors and a billionaire hedge fund manager who played a key role in the Brexit campaign are both braced for revelations about their financial affairs, The Telegraph can disclose as a second company is revealed as a victim in the offshore Bermuda hack.

Lord Ashcroft, who has given millions to the Tories, could see his company's financial deals exposed as he is a client of a company which has been caught up in a huge data leak.

The dealings of Robert Mercer, a major donor to Donald Trump who also aided the Leave.EU campaign, could also come under scrutiny following the attack on one of the world's biggest offshore law firms.

The men are the first to be named in connection with hack on Appleby, first disclosed by The Telegraph, files from which are expected to be published by an international group of left-leaning journalists on Sunday.

The news that Lord Ashcroft could be among those named will be potentially embarrassing to the Conservative party because of sensitivities surrounding legitimate off shore tax avoidance schemes. The leak comes a year after the "Panama Papers" exposed the hidden millions of politicians, celebrities and some of the world's richest businessmen.

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Lord Ashcroft - former deputy chairman and party treasurer - has donated millions to the Conservatives over the years and - after a brief hiatus prompted by a falling out with David Cameron - he gave £500,000 to the party in the run up to this year's General Election.

Waterloo Holdings Ltd, of which Lord Ashcroft is the principle shareholder, is sponsored to list on the Bermuda Stock Exchange by Estera, which is an offshoot company of Appleby. Estera became independent in January 2016 but continued to use the IT services of its former parent company and it is understood when Appleby's servers in Bermuda were hacked some Estera’s client details were also breached.

They informed the regulators in Bermuda and their clients immediately, a source close to the company said. Although it is legitimate to hold offshore accounts, because of the furore over David Cameron's father holding overseas trusts - which was exposed as part of the Panama Papers - the Party are likely to be sensitive about any links they have to individuals who home accounts in Bermuda.

Robert Mercer, whose company Cambridge Analytica helped win the anti-EU vote and who donated $25 million to groups supporting the current US president, oversees at least five multi-million dollar investment vehicles legally registered in Bermuda by Law firm Appleby.

Robert Mercer and Rebekah Mercer attend the 2017 TIME 100 Gala at Jazz at Lincoln Center in New York credit: Getty Images

The total value of the funds is believed to be in excess of $2.7 billion, according to documents filed with the United States' Securities and Exchange Commission. The largest - Renaissance Institutional Futures International Fund LP - has sold shares worth more than $1. 6 billion. An additional fund with shares worth more than $68 million was registered by Estera. All six funds were founded between 1997 and 2012, with returns filed as recently as May this year in four cases.

The prominent Republican party supporter’s name appears alongside that of his company, Renaissance Technologies LLC, which has its headquarters in New York. A spokesman for Renaissance Technologies declined to comment. A spokesman for Lord Ashcroft said that "to the best of everyone’s knowledge" Waterloo Investment Holding Ltd had not been impacted by the hack. He said that much of the company data was already public and there was "little concern about Waterloo and it shareholders".

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Appleby and Estera have both denied any wrongdoing on behalf of their companies and their clients and both companies said they were committed to protecting their clients’ data.

Appleby said: "We will continue to defend ourselves and our legitimate and lawful business against groundless allegations."

Dame Margaret Hodge, Labour chair of the All Party Parliamentary Group on Responsible Tax, said: “We will get an endless stream of leaks until some time as our government and the overseas territories understand the absolute fury that everybody feels when very rich individuals or big corporations use secret financial structures to either avoid or evade tax.

“However, Britain is currently refusing to do anything to upset any country that isn’t part of Europe”.