When Lord Ashcroft was treasurer of the Conservative party he listened patiently to the director of a charity give a talk on how to raise money before realising such methods would never work in the world of politics.

“I will send £20,000 to your charity if you are out of the room in 30 seconds,” Ashcroft told him. The man picked up his charts and was gone. Ashcroft sent the cheque.

Charities stand to gain much more on his death. He has announced that he is to give more than 80% of his wealth to good causes.

As his personal fortune is estimated at £1.1 billion, it could be the biggest charity bequest made in Britain.

Both Lord Sainsbury, the former science minister and Labour’s biggest donor, and Sir Tom Hunter, the Scottish entrepreneur, have pledged to give away £1 billion, but their fortunes are tied to the vagaries of the stock market and have fallen in the recent collapse in share prices.

Ashcroft announced his bequest in a new epilogue to his book Dirty Politics, Dirty Times, published on his website. An update states: “I have prepared my will. I have never been a great believer in inherited wealth. More than 80% of my assets — and I never discuss how much I am worth — will be left to a charitable foundation in my name.”

He adds: “My family will be trustees so that they can enjoy spending money on worthy causes in my name. The balance of my assets will be left to my family.”

Ashcroft is a controversial figure who has faced questions over the last year on whether he is domiciled in the UK for tax purposes. The Sunday Times revealed in September how he channelled money from the heart of his business empire in Belize into Tory party funds, despite a ban on overseas donations. The scheme exploited a loophole in the current law, but the Electoral Commission is now reviewing the evidence after complaints from MPs.

His first significant move into charitable work followed the murder of PC Keith Blakelock during the Broadwater Farm riots in north London in 1985: he offered a £10,000 reward for information leading to the arrest of the killers.

In 1988 he launched Crimestoppers, which provides confidential telephone lines on which people can leave information about those they suspect of having committed crimes.

The charity celebrated its 20th anniversary with its one millionth call last summer. So far the calls have led to more than 86,000 arrests, the recovery of £102m of stolen property and the seizure of £151m worth of drugs.

In July Ashcroft announced a donation of £5m for a new gallery at the Imperial War Museum to house his collection of 155 Victoria Cross medals, the largest in the world, alongside the museum’s own display of 50 VCs.

When he was president of the London City Ballet and Diana was its patron, he held a fundraising evening at Wembley greyhound stadium. The princess was to present a trophy to the winner of one race. As they approached the triumphant dog, Ashcroft whispered: “Ma’am, it’s a tradition at this point that you lift the tail of the winning greyhound.” She reached forward with one hand and was about to do so when Ashcroft said: “I’m only joking, ma’am.”

Two years ago he held his 60th birthday party at the Grosvenor House hotel, which was decked out to resemble a tropical paradise reminiscent of Belize. The 700 guests, who included David Cameron and the shadow cabinet, donated £200,000 to Crimestoppers.

Ashcroft said yesterday that he had already made plans for how his money will be shared.

“A combination of both professionals and family will decide how to spend the money. I can express wishes. I think it will be reasonably well known the direction in which I would want the foundation to go,” he said.

Lord Tebbit, another Tory grandee, said: “Michael Ashcroft is a very generous man. I would hope a great part would go to education, where I know his heart is.”

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