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 361. 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 42. 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.
