Senedd Research Service

The Senedd Research Service is the official research and information unit of the Senedd (Welsh Parliament). It provides impartial analysis, briefings, and committee support to Members of the Senedd (MSs), covering Welsh legislation, policy areas, and electoral matters. Senedd Research operates to the same impartiality standards as the House of Commons Library at Westminster.

Its 2025-2026 briefings on the closed-list D'Hondt seat allocation for the new 96-seat Senedd are the primary public explanation of how the 2026 electoral system will distribute seats. Senedd Research estimates a party needs roughly 12 per cent of the vote in a constituency to win a single seat under the new six-member-constituency D'Hondt allocation, which has become the benchmark figure used by UK electoral modellers for Welsh 2026 projections. Senedd Research also publishes analysis of the gender-representation implications of the system following the September 2024 withdrawal of the gender-zipping bill.

The Senedd Research Service's 12 per cent threshold figure has done more to shape electoral analysis of the 2026 Welsh election than any single piece of research from outside the institution: it is the calibration point that turns raw polling percentages into projected seat counts. For readers assessing whether smaller parties can break through in Welsh constituencies, that single estimate is where the analysis has to start.