Landmark legislation to increase the size of the Senedd and change its voting system cleared the final hurdle in the Welsh Parliament.

MSs voted 43-16 in favour of the members and elections bill, securing a necessary two-thirds supermajority, following a debate on 8 May.

Under the bill, the number of Senedd members will increase from 60 to 96 in response to concerns that the relatively small size of the legislature leads to ineffective scrutiny.

The maximum number of Welsh Government ministers will increase to 17 – not including the first minister and counsel general – with powers to further increase this to 19.

The 32 constituencies in Wales that will be used in the forthcoming general election will be paired to create 16 for the 2026 Senedd poll, with each returning six members.

Mick Antoniw, who is counsel general, the Welsh Government’s chief legal adviser, said Welsh democracy has grown, developed and matured over the past 25 years.

Mr Antoniw told the chamber that while the responsibilities of the Senedd have grown, its capacity has not – remaining the smallest of the UK’s devolved legislatures.

“The bill before us changes that,” he said. “It is a once-in-a-generation opportunity to invest in our democracy by creating a modern Senedd.”

Mr Antoniw said the bold reforms will give the Senedd greater ability and capacity to hold the Welsh Government to account as well as ensure that every vote counts.

He argued laws are best forged in the fires of parliamentary scrutiny, saying: “I think we’ve seen that in this bill’s own legislative passage.”

Darren Millar, who is the Conservatives’ shadow constitution minister, described the bill as a deeply flawed piece of legislation which will undermine Welsh democracy.

Wales will move away from the current additional-member electoral system which uses a mix of first-past-the-post constituencies and regional party lists.

Future Senedd elections will instead use a full form of proportional representation, with Wales becoming the first UK nation to entirely scrap the first-past-the-post system.

Under the new closed-list system, People will vote for political parties rather than individuals and parties will control the order of candidates on lists.

Mr Millar, whose party was alone in voting against the bill, said the reforms will damage the relationship between the public and their elected representatives.

He told the Siambr the closed-list system will strip away a fundamental right enjoyed by generations of Welsh voters to choose an individual candidate.

The Tory MS for Clwyd West said: “It is the biggest power grab from the people of Wales that it has ever suffered in the history of Welsh democracy.”

Mr Millar criticised the “shameful” costs of expansion which have been estimated at almost £18m a year, suggesting it would be better spent on schools and hospitals.

He said: “That money instead will be spent on luxury offices and pay for 36 more politicians, their entourage of staff and the structure needed here at the Senedd to support them.

“Spending £120m on more politicians over the review period is a luxury we can ill afford.”

‘Long awaited’

Heledd Fychan, for Plaid Cymru, said the long-awaited reforms will strengthen opposition members’ ability to hold Welsh ministers accountable.

Ms Fychan, who represents South Wales Central, stressed that the reforms are not the end of the journey, with a review to follow the 2026 election.

She said Plaid Cymru will continue to support – and campaign for – the single-transferable vote (STV) electoral system, which would allow voters to rank candidates.

Ms Fychan added that her party will hold the Welsh Government to a commitment to bring forward a recall system, which would allow voters to remove members between elections.

She said: “There is still work to be done to strengthen our democracy but the step that we are taking today is a huge step forward – not only for this Senedd but also for our nation.”

Jane Dodds agreed the bill will enhance scrutiny as well as ensure proper representation for each and every one of Wales’ diverse communities.

The Lib Dems’ leader in Wales welcomed the “outdated” first-past-the-post system being binned but warned the proposed replacement is fundamentally flawed.

Ms Dodds said: “The introduction of closed party lists risks robbing voters of true choice.”

The Mid and West Wales MS argued STV would be the fairest and most accountable system, with every vote carrying equal weight and power.

Ms Dodds said she would support the legislation but she urged fellow members to view it as only the first step on a journey towards a stronger, fully democratic parliament for Wales.

Mike Hedges, a Labour backbencher who represents Swansea East, pointed out the practical problems of having as few as four members on some Senedd committees.

He said that day’s public accounts committee meeting would have had insufficient members to proceed if he had to go to the toilet, warning: “You cannot run an organisation like that.”

Mr Hedges described the reforms as akin to reverse gerrymandering, suggesting Labour will find it hard to win and the new system will consistently produce a hung Senedd.

The bill is expected to receive Royal Assent, officially becoming an Act, later this year.

MSs are considering two related bills: the elections bill, which would introduce automatic vote registration, and the candidate lists bill on gender quotas in Senedd elections.