YouGov's final Senedd MRP (fieldwork 25 April–4 May 2026, n=4,600+) projects the Wales Green Party at 2 seats — both in Cardiff — down from 10 seats in YouGov's first Senedd MRP three weeks earlier. Plaid Cymru projects at 43 seats (33% vote share), Reform UK at 34 (29%), Welsh Labour at 12 (12%), Conservatives 4, Lib Dems 1. A Plaid-Labour majority holds in 89% of simulations. YouGov attributes the 8-seat Green collapse primarily to a Green-to-Plaid migration in the final fortnight. More in Common's final Senedd MRP ties Plaid and Reform at 34 each, with Labour third on 14.
An 8-seat Green collapse before any ballot is cast is the first electoral-system event of the 2026 night, and it shows how D'Hondt allocation rewards bloc consolidation over pluralism in the first British election to use closed-list PR.
