History. 3 of 6: nothing out by 31 December (Theresa May on industry 2016, Theresa May on social care 2017, Johnson on levelling up 2021).
Hunch. On 5 November Andy Burnham said himself that the plan may go into the new year and that there is no firm date for it yet.
The 31 December market resolves YES if by 23:59 London time on 31 December 2026 GOV.UK shows no document, published after 6 November 2026, that GOV.UK or No 10 itself presents as the Prime Minister's 10-year plan for Britain, in any spelling, with BBC News and The Guardian as backup. A document that opens a consultation counts, while a speech or press release page alone, a document on one part of the plan, or a document with only '10 year' in its title does not.
We looked for cases where a UK prime minister promised a major government document and said it would come by the end of the year. We found six, from 2012 to 2021. Three came out in time. In the other three nothing was out by 31 December.