History. No count from the cases: none recorded a Commons vote forced by allies. This question comes from what the two sides want.
Hunch. About 100 Labour MPs have already backed a Commons amendment on a commission, and the Liberal Democrats want a new system before the 2029 deadline (BBC News, 29 Sep 2026). Editorial scoring note: The conditional sample has four promises without a chair already named: one chair was named within 30 days. The already-named-chair and no-commission rows are context; wider commission groupings are not this denominator.
The Commons vote market resolves on 18 December 2026 at 10:00 in Hansard and on votes.parliament.uk: YES if by 17 December 2026 the Commons divided on a motion, amendment or bill calling for a different voting system for the Commons or a referendum on one. A debate or first reading without a division, or a vote in the Lords, resolves NO.
We looked for cases where a British leader whose party held power under a set of rules (voting system, the Lords, devolved powers) promised to change them, then handed the choice to a commission or a public vote, with no change in law before the next election. We found six, from 1997 to 2016. Only three are about the voting system; the others are about the House of Lords and Scotland's powers. The Jenkins and Wakeham commissions came from one 1997 Labour manifesto, so they count once. In the four where no chair was named on the day, as with Burnham, one had a chair within 30 days.