A farmer’s son inspired to join the Tories by Margaret Thatcher has been elected Conservative leader at the Welsh assembly.

Paul Davies called for his party to offer a radical alternative to Labour, which has held power in Wales since the first assembly elections in 1999 after devolution.

Davies won 68% of the vote, while his opponent Suzy Davies (no relation) picked up 32%. He replaces another Davies, Andrew RT, who unexpectedly stepped down after seven years in the job following controversy over his Brexit stance.

In his acceptance speech, delivered partly in Welsh, Paul Davies said he was a boy from the “traditional heartlands of west Wales” and that the party had a mountain to climb if it was to win power.

“It’s time for us to raise our game,” he said, but added: “We have a duty to offer the people of Wales a progressive, innovative and radical alternative.”

He pointed out that Wales had never returned a female Conservative MP and said the party needed to be more representative of Welsh society and at the next assembly elections offer a “diverse slate of candidates from all walks of life”.

Davies said he respected the result of the EU referendum and would oppose any party or person who attempted to block the “will of the people”. But he added that he would work with the UK government to deliver the best Brexit deal for Wales.

The prime minister, Theresa May, tweeted her congratulations:

Congratulations to @PaulDaviesPembs who has today been elected Leader of @WelshConserv in the Welsh Assembly. There has never been a more vital time for us to hold the failing Labour-run Welsh Government to account. I know he’ll do a fantastic job speaking up for the Welsh people — Theresa May (@theresa_may) September 6, 2018

Andrew RT Davies resigned in June amid criticism from within his party over his vocal pro-Brexit stance. He campaigned strongly for the UK to leave the EU, causing embarrassment to the then prime minister, David Cameron. Shortly before stepping down he was highly critical of the warning by Airbus, a key employer in Wales, that it could cease manufacturing in the UK because of Brexit, dismissing the claim as “hyperbole”.

During the race to replace him, Paul Davies said he would be prepared to speak to other parties about working together to oust Labour in Wales.

Davies, who is the assembly member for Preseli Pembrokeshire, has also called for the role of the leader in Wales to be clarified. There has been a dispute within the Tories about whether the leader should be regarded as the head of the Conservatives in Wales or simply as the boss of the assembly group.