YouGov's second 2026 Senedd MRP, with fieldwork from 6 to 15 April on 2,387 Welsh adults, projects Reform UK on 37 seats and Plaid Cymru on 36 1. Both parties share 29% of the vote on central estimates. Welsh Labour is unchanged on 12, the Wales Greens drop from 10 to 7, the Welsh Conservatives rise from 1 to 3, and the Welsh Liberal Democrats take 1.
The first MRP, in March, had Plaid on 43 and Reform on 30 . The seat swing across six weeks is fourteen: seven from Plaid to Reform, plus three lost from The Greens. Yet the same fieldwork puts both parties on identical 29% vote share, suggesting the swing is geographic rather than aggregate. The Plaid-Green coalition arithmetic that opened the left's route to a 49-seat majority is no longer in the model. A Plaid-Green combination now reaches 43 seats, six short. A Plaid-Labour combination reaches 48, one short. All three left-leaning parties together carry a majority in 96% of simulations, but require active cooperation among parties already arguing publicly about who counts as left in Wales .
Two other models broadly corroborate the closeness without matching the YouGov reversal. Ipsos's Wales poll on fieldwork to 8 April puts Plaid on 30%, Reform 25, Labour 15. More in Common's Senedd MRP projects Plaid 30, Reform 28, Labour 24, Greens 4 2. Three independent models agree on one thing: no party wins a Senedd majority alone. They disagree on which of Reform or Plaid finishes first, and on whether The Greens cross the entry threshold.
Wales is using closed-list proportional representation for the first time , with 16 six-member constituencies and the D'Hondt allocation method (votes divided by 1, 2, 3 etc., seats awarded to highest quotients). Closed-list PR registers small movements between adjacent parties contesting the same ideological space sharply. The 7-seat shift from Plaid to Reform reflects under three points of Welsh vote share moving across that line. The system is doing what it was designed to do; Welsh voters are watching it for the first time.
