The six men and women who have been UK prime ministers seldom mix together except for solemn occasions such as funerals and Remembrance Sunday.

The dinner to mark a century of prime ministers living at Chequers this weekend is not going to be the cheerful joint celebration which the mansion's trustees were hoping for.

Four of the living premiers - David Cameron, Gordon Brown, Tony Blair and Sir John Major - have turned down their invitations, pleading previous engagements.

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