Work to expand the Senedd’s debating chamber to accommodate more politicians will cost the public purse an estimated £4.22m – up nearly 30 per cent on an initial estimate.

Construction work on the chamber began this year with the Welsh Parliament set to expand from 60 to 96 members at the next election in May 2026.

The Senedd commission earlier estimated the total costs of chamber-related works at £3.25m, according to its response to a freedom of information (FoI) request in May 2025.

Now, the commission – which is the corporate body responsible for the Senedd estate and support services – has confirmed the refurbishment will cost taxpayers nearer £4.22m.

During questions to the commission on 24 September, James Evans asked for an update on the costs of the new chamber and expected timelines for completing the work.

Elin Jones, the speaker or Llywydd, was confident Senedd members would return to the new Siambr following the spring half term in late February.

Ms Jones said: “The latest estimate for the full costs of the works is £4.22m.

“This cost will be fully funded from the Senedd reform budget for this current year.”

Mr Evans responded: “I’m totally against Senedd expansion and the spending of that £4.22m as you’ve outlined.”

The Conservative added: “It’s important if we are spending that money that we are making sure Welsh businesses are benefiting from the work that is being done and we’re using Welsh materials, so that money is being reinvested back into our economy.”

Ms Jones said all public tendering work was clear about the commission’s preference for Welsh companies and materials.

She confirmed the main contractor is Welsh.

Politicians have moved to Siambr Hywel in Tŷ Hywel, the red-brick building linked to the Senedd by glass walkways, while work is ongoing.