The Conservatives are enduring a “challenging” election, Scottish Tory leader Douglas Ross has admitted.

The outgoing party chief, who will stand down after the 4 July vote, said a scandal over senior Conservatives allegedly placing bets on the date of the ballot was “unacceptable”.

However, he backed Prime Minister Rishi Sunak’s decision not to suspend those under investigation by the Gambling Commission, including two candidates.

Mr Sunak said his party was carrying out a “parallel” internal inquiry.

Mr Ross said the party’s issues during the election campaign had been “well rehearsed”.

He announced in the early stages of the campaign that he would step down at Scottish Tory leader following the vote.

It came after he was controversially selected to stand for the Aberdeenshire North and Moray East seat instead of David Duguid, who has been in hospital and was effectively de-selected.

“I’m the leader of the party and I take responsibility for how the party does and my own actions,” Mr Ross told BBC Radio’s Good Morning Scotland.

Mr Sunak, who joined Mr Ross in Edinburgh on Monday to launch the Scottish Conservative manifesto, has come under pressure to suspend members under investigation from the Gambling Commission.

The commission has not said who it is investigating but so far the names of four Conservatives have emerged – including two who are standing for election.

Mr Ross said it was important the investigation was not “hindered”, adding: “People have a right to defend themselves.”

It was put to the Scottish Tory leader that one Conservative candidate, Craig Williams, had admitted to and apologised for placing a bet.

Mr Ross said the party had to “look at all the circumstances”.

He told BBC Scotland that if anyone was found to have “used their position or information they held to place a bet and gain financially from that then they should have no place in the Conservative Party”.

The party chief added: “I think the scandal has been an unacceptable incident in the campaign and I want the Gambling Commission to do their job as quickly as they can to look at all the details and come to a conclusion.”

Asked why people should vote for the Conservative Party in the wake the betting scandal, years of leadership turmoil and an error-prone election campaign, Mr Ross said: “We have made progress but there is more to do and the prime minister and the UK government have taken difficult decisions to turn our economy around and deal with the big decisions.”

He said that was in “stark contrast” to what is being offered by Labour and the SNP.

Mr Ross, who had been serving as an MP at Westminster and MSP at Holyrood, had u-turned on his decision to step down from the UK Parliament at this election.

But following criticism over his decision to stand, he has said it would no longer be “feasible” to do both roles, as well as being party leader.

Mr Ross – who is also a professional assistant football referee – has said he will quit as an MSP if he is successfully elected to Westminster.