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

Multiple recent MRP seat projections (YouGov March: Plaid 43 seats; Beaufort March: 37; UK-Elect April 8: 37) consistently show Plaid Cymru winning the most seats out of 96, ahead of Reform UK by 6-13 seats, with vote leads of 3-6%. No projections indicate otherwise, and with only three weeks until the May 7 election, the true probability of Yes exceeds 85%, providing a positive edge on the 80% price. The low volume ($8k) suggests limited sophisticated pricing, confirming the mispricing.

Recent polls (e.g., Beaufort Research March 2026: Plaid 30% vs Reform 27%, projecting 37 vs 30 seats; YouGov MRP March 2026: Plaid 33% vs 27%, 43 vs 30 seats) and polling averages (PollCheck April 1: Plaid 28.4% vs Reform 27.6%) consistently project Plaid Cymru to win the most seats due to constituency strength, indicating a true Yes probability well above 80% despite close vote shares. The 80% Yes price appears mispriced low given the stability 3.5 weeks from election, offering actionable edge. No evidence of recent shifts favoring Reform.

Recent YouGov MRP polling from March 2026 shows a seismic shift in Welsh politics, projecting Plaid Cymru to win 43 seats, well ahead of Reform UK (30) and Labour (12). This data, combined with the new proportional representation system (D'Hondt method) being used for the first time in 2026, significantly favors Plaid Cymru's concentrated regional support over Labour's collapsing vote share. External betting markets have Plaid Cymru as heavy favorites at 1/5 (83.3% implied probability), suggesting the current 80% price on Polymarket still offers a slight edge given the strength of the polling consensus and the structural advantages of the new electoral system for the leading party.