EDINBURGH (Reuters) - British Prime Minister Rishi Sunak said on Monday he would act on any findings of wrongdoing from an internal investigation into a damaging betting scandal that could punish him further at a July 4 election he is expected to lose.

His Conservative Party trails the opposition Labour Party by around 20 points in UK polls and Sunak's campaign has failed to take off amid a series of mis-steps, including his decision to leave D-Day commemorations early.

The campaign has been further damaged by revelations that several party officials and candidates are being investigated for allegedly betting on the date of the election before it was announced.

Sunak has said he was "incredibly angry" to hear of the allegations, which are being investigated by the Gambling Commission, and told reporters he was not aware of any other candidates being investigated.

"We have been in parallel conducting our own internal inquiries, and will of course act on any relevant findings or information," Sunak told broadcasters after a campaign event in Edinburgh.

Labour leader Keir Starmer criticised Sunak's handling of events, saying it showed weakness.

"Rishi Sunak needs to show some leadership," he told reporters. "If these were my candidates... they'd be gone".

'INDEPENDENCE ON THE BACKBURNER'

In Scotland, Labour hope to capitalise on the struggles of both the Conservatives and the pro-independence Scottish National Party (SNP), who are on their third leader in little over a year.

The SNP have dominated the Westminster parliament's Scottish seats since 2015, garnering support of pro-independence voters in the wake of a 2014 referendum where Scots voted to remain part of the United Kingdom by 55% to 45%.

But a police probe into the SNP's finances, Nicola Sturgeon's sudden resignation as leader last year and the implosion of her successor Humza Yousaf's administration in the devolved Scottish government this year have put that dominance in question.

Labour has also regained momentum in its former Scottish heartlands and polls show it level with or even ahead of the SNP for the first time in a decade.

The SNP manifesto says that if it wins a majority of Scottish seats, it will begin negotiations on independence, though both Sunak and Starmer have ruled out such talks.

At the launch of the Scottish Conservative manifesto, Sunak aimed his speech almost entirely at the SNP and their attempts to pursue a second independence vote.

The Conservatives are trying to hang on to their six Scottish seats, where the SNP are their main rivals.

"The fourth of July is Scotland's chance... to put independence on the backburner for a generation," Sunak said.

"But that can only happen if the SNP are routed. If they do not just lose some seats, but the SNP lose big."

He also criticised the SNP and Labour's approach to the energy sector, saying the Conservatives were the only way to protect North Sea oil.

The Conservatives lag behind in third place in Scotland, and could be on course for a historic defeat across the UK as a whole. Research by Ipsos Scotland found Sunak has a net negative approval rating of -64 points.

"We see Westminster politicians take campaign trips north of the border to dismiss the very idea that Scotland can have real, genuine influence at Westminster," SNP leader John Swinney said in extracts of a speech he is due to give on Monday.

"Scotland's voice is still ignored and our democratic choices are still disrespected."

(Writing by Alistair Smout; Editing by Andrew Heavens)

By Phil Noble