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

Construction work on the chamber – known as the Siambr – 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 today’s (September 24) questions to the commission, James Evans asked for an update on the costs of the new chamber and expected timelines for completing the work.

‘Fully funded’

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, who represents Brecon and Radnorshire, 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.

‘Committed’

Politicians have moved to Siambr Hywel in Tŷ Hywel, the red-brick building linked to the Senedd by glass walkways, while work is ongoing to accommodate 36 more members.

Senedd members moved back into Siambr Hywel – where the then-National Assembly for Wales met from 1999 to 2006 – in April 2025.

The work includes removing the back wall to make more space, replacing the back corridor with small lobbies and removing steps to make the Siambr more accessible. Desks will be installed for 96 members – with a refit of circulation, lighting and audio-visual systems.

The second and third floors of Tŷ Hywel are also being reconfigured to create more offices.

Over the summer, in response to a separate FoI request, the Senedd commission committed to publishing an itemised list of the spending on refurbishment in autumn 2025.