Jonathan Ashworth, Labour’s shadow paymaster general, jumped on Mr Sunak’s refusal to rule out that a Cabinet minister could be involved. He said: “Today Rishi Sunak has refused to rule out that further members of the Conservative Party, including Cabinet ministers, are involved in this betting scandal. He needs to come clean with the public.

“He promised integrity, professionalism and accountability, instead his weakness means he has overseen the same levels of sleaze and scandal that have come to epitomise the last 14 years of Tory government.

“Rishi Sunak needs to take immediate action against all implicated.”

Angela Rayner added that the Prime Minister “should reveal what he knows about what happened – and also I find it astonishing that action hasn’t been taken in regards to that”.

It comes as polling by YouGov found that the Conservative betting scandal was the one of the news stories about which the British public were most aware this week.

Some 17 per cent of respondents said they had noticed the story, compared to 8 per cent being aware of coverage of the European Championship.

Mr Sunak has insisted that if anyone is found to have broken the rules they will be thrown out of the Conservative Party, but he said it was important to wait for the outcome of the investigation.

‘Betting on inside info stinks’

On Friday, Tom Tugendhat, the security minister, expected to run for the Tory leadership at the next contest, told The Telegraph: “Betting on inside information stinks. It’s wrong and those involved must go.”

A Conservative spokesman said: “We have been contacted by the Gambling Commission about a small number of individuals.

“As the Gambling Commission is an independent body, it wouldn’t be proper to comment further until any process is concluded.”

In a statement, Ms Saunders’ solicitor said that she would be cooperating with the watchdog’s investigation.

The statement added: “It is inappropriate to conduct any investigation of this kind via the media, and doing so risks jeopardising the work of the Gambling Commission and the integrity of its investigation.”

A spokesman for the Gambling Commission said: “Currently, the commission is investigating the possibility of offences concerning the date of the election.

“This is an ongoing investigation, and the commission cannot provide any further details at this time.

“We are not confirming or denying the identity of any individuals involved in this investigation.”