Unanswered General Election question: who'll be through the door first?

One question not being posed during the General Election is: which - if any - former prime minister will be the first to visit Downing Street after the election?

Famously, Margaret Thatcher visited Tony Blair after the 1997 General Election. The election was held on 1 May. The meeting between the two prime ministers took place on 22 May. It was reported in The Sunday Times on 25 May. Correspondence in The National Archives between the Director of Lady Thatcher's office, Julian Seymour, and Blair's Chief of Staff, Jonathan Powell, dated 7 May, revealed the subjects to be covered including Europe, Asia, China and the handover of Hong Kong.

Lady Thatcher also famously - and controversially - visited Gordon Brown in Downing Street in September 2007. Unlike the initial meeting with Blair, the press was on hand to witness her arrival and departure. In September 2008, she had lunch with Brown at Chequers. In November 2009, she returned to Downing Street for the unveiling of her portrait.

Lady Thatcher also visited Downing Street in June 2010, not long after David Cameron was appointed Prime Minister. 

She was not the only former prime minister to meet a predecessor of another party. John Major became Prime Minister on 28 November 1990. His manuscript diary for 6 November 1990, released by The National Archives in June 2023, reveals a meeting with Lord Callaghan at 6.15pm that day.