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That fascinating detail is revealed as that first contract, from November 1, 1946, comes up at the Graham Budd auction in London on May 21- 22 estimated at £30,000-40,000.

Along with clauses such as a fixed annual salary of £675, it states he was to “use all proper means in his power to further the quality of play of the teams and the attractiveness of their football”.

This contract was a game-changing moment for United. As Budd says: “It changed the history of that club – they hadn’t been great for a long time at that stage and certainly Man City, who Busby had played for, ironically, were certainly the better team, winning an FA Cup [1933-34] and the league [1936- 37] in the 30s.” With United, Busby won five league titles and two FA Cups, and in 1968 they became the first English club to lift the European Cup.

Budd adds: “The contract did go to auction at Phillips in the 1990s when the football memorabilia market was still in its infancy, and it made £4200 hammer. At the time that was a lot of money in the football market – no major collections had come up at that time.”

The person who bought the contract back then, a private collector, consigned it to Graham Budd. The contract is thought to have been spotted by the original vendor at Phillips when Man United were having an administrative clear-out.