Reform UK’s Dan Thomas has quit as the party’s Welsh leader after he was arrested on Sunday on suspicion of assault and controlling or coercive behaviour.

Gwent Police confirmed that a 45-year-old man from Aberbargoed, in Caerphilly, has been bailed pending further enquiries.

Reform said in a statement Thomas was “standing down” from his position for “personal reasons”, with a meeting to be held on Wednesday to start the process of finding Thomas’s replacement.

Thomas said he had been “released without charge” and had “done nothing wrong”.

He was appointed Welsh party leader by Nigel Farage in February.

Plaid Cymru, which runs the Welsh government, said: “Reform UK is descending into chaos.”

Thomas did not take part in First Minister’s Questions on Tuesday.

He was first elected to the Senedd in the elections in May, where his party went from having two politicians in Cardiff Bay to 34.

Reform came second behind Plaid Cymru in the vote, with Thomas becoming leader of the opposition in the Senedd.

Thomas said: “It has been the honour of my life to have been the leader of Reform Wales and see this party go from zero to 34 elected members and become the largest opposition group in Welsh history.

“With deep regret, I am now standing down from this position due to personal reasons.

“Over the weekend, I was reported to the police and was released without charge.”

He added: “I will continue to serve my constituents in Casnewydd Islwyn and will fully back whoever the group selects as its next leader.”

The news came on the same day that Reform MS Sarah Cooper-Lesadd defected to Plaid Cymru.

Gwent Police said: “On Sunday, 13 September a 45-year-old man, from the Aberbargoed area, was arrested on suspicion of assault and engaging in controlling/coercive behaviour.

“He has been bailed pending further enquiries.”

Reform MS Llyr Powell said a meeting will be held on Wednesday to start the process of finding a new leader of the party.

He confirmed that Reform’s Welsh deputy Helen Jenner will be interim leader until a decision is made on who will take over from Thomas.

Speaking on Thomas’s decision to step down as party leader, Powell told BBC Radio Wales Breakfast: “I think it’s right that Dan stepped down for the party to remove any distraction that’s there and even for his wellbeing and his family.”

When asked if Thomas should remain in the party, Powell said: “As it stands, the police are doing their investigation. It would be wrong for me to get involved, trying to presume anything of that. So, right now, Dan is a member of the Senedd.”

Plaid Cymru Senedd group chair Marc Jones said: “Reform UK is descending into chaos.”

He added: “Sarah Cooper-Lesadd’s decision to leave and join Plaid Cymru says it all – Reform is interested in division and headlines, not governing Wales.”

Ken Skates, leader of Welsh Labour, told the Press Association: “This is quite incredible news and many questions will need to be answered.

“Dan Thomas was a personal pick by Nigel Farage and this will surely demonstrate the appalling judgement of the Reform UK leader.”

Mims Davies, Conservative Shadow Secretary of State for Wales, said: “Reform are hitting the news for all the wrong reasons – massive crypto donations, on top of the jailing of Nathan Gill for pro-Russian bribery.

“All this raises serious and deep questions about Reform’s judgement and leadership at every level.”

Welsh Liberal Democrat Leader Jane Dodds said: “The wheels are rapidly coming off Reform in Wales and the entire country.”

Thomas grew up in Blackwood in the south Wales valleys.

He said in February that both his grandfather and great-grandfather were miners, and he had “fond memories” of growing up in Wales – but left when he became an adult because “good opportunities” there were “few and far between”.

He worked in financial services in London and became a councillor, and later Conservative leader, at Barnet council in the north of the capital.

During this time Thomas stood for the Conservatives in the Islwyn constituency at the 2010 and 2017 general elections, coming second to Labour’s Chris Evans on both occasions.

Thomas then led Barnet council from 2019 to 2022, eventually becoming opposition leader after Labour won the local election there until May 2024.

In June 2025 Thomas defected from the Conservatives to Reform, and at the end of the year resigned from the council.

Local media quoted him saying he moved away from Barnet so that he and his wife could raise their young sons in the countryside and live closer to their families in south Wales.