Will Plaid Cymru win the most seats in the 2026 Welsh Senedd election?

“Plaid Cymru leads in every recent poll: the May 5 ITV/YouGov poll (two days before voting) shows Plaid at 33% vs Reform 29%, translating to 43 seats vs 34 seats under D'Hondt. The PollCheck 5-poll rolling average (May 5) has Plaid 30.0% vs Reform 27.6%. No recent poll shows Reform clearly ahead.. Labour's historic collapse from 36% (2021, 30 seats) to ~12-14% projected removes the traditional dominant party from contention, making this effectively a two-horse race in which Plaid holds the lead. The Caerphilly by-election (Oct 2025) — Labour's first loss there in 100 years — with Plaid winning 47% vs Reform 36% demonstrated Plaid can beat Reform head-to-head in working-class seats..”

“The bull overstates the polling signal. A 2-4 point vote lead in a brand-new electoral system is not remotely enough to justify 0.82 YES. The research itself includes a YouGov MRP with Reform on 37 seats to Plaid's 36 and a More in Common model with 34-34. When credible late-cycle models include ties or a Reform edge, the evidence base is 'coin-flip to modest Plaid edge,' not 'Plaid highly likely.'. The bull's structural read of D'Hondt is too confident and partly misleading. In 16 six-member constituencies, plurality in votes does not linearly guarantee plurality in seats; the decisive seats are often the 5th/6th seats, which are highly sensitive to local distribution and threshold effects. The research explicitly says the sixth seat in each constituency may be decided by handfuls of votes. That creates seat volatility, which hurts any thesis built on a small national polling edge..”