The former prime minister John Major was warned three decades ago how Sir Winston Churchill’s private archive could be broken up unless he approved buying it with National Lottery money, newly-released government files show.

The World War Two leader’s papers were bought from the Churchill family trust for £12.5m in 1995 and archived at Churchill College, Cambridge.

Beneficiaries included Churchill’s grandson, also called Winston Churchill, who was a Conservative MP.

Documents released by the National Archives show the concerns government officials had over the purchase at the time.

Under the terms of an agreement about a million documents would be preserved at the archive centre at Churchill College.

The lottery’s National Heritage Memorial Fund would pay £11.5m with the remainder coming from the J Paul Getty Trust.

The former prime minister Boris Johnson, who was a columnist on The Daily Telegraph at the time of the purchase, was among the critics of the use of lottery money.

He described the purchase as “taking from the poor to give to the rich”.

The then lord chancellor, Lord Mackay of Clashfern, also had concerns.

But the released papers show that the cabinet secretary at the time, Sir Robin Butler, had explained how, in part, lottery money was being used to avoid the risk of future litigation.

“The £12.5 million referred to represents not only the purchase price for the purely private material but also an element of buying out the risk of litigation in which counsel assessed our chances of success as, at best, 50/50,” he had written.

“We are advised that we should proceed with the transfer as planned… and that delay could result in the collapse of the whole arrangement.

“This could lead to a break up of the archive, which is what we have been trying very hard to prevent.”

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