Embattled Home Secretary Suella Braverman has been referred to a financial watchdog by Labour over concerns of a breach of insider trading laws.
Shadow city minister Tulip Siddiq has asked the Financial Conduct Authority to investigate the leaking of information that led to Ms Braverman's resignation.
Rishi Sunak has been under sustained pressure since deciding to reappoint Ms Braverman to the role six days after she was forced out by Liz Truss while she was still prime minister.
Without authorisation, Ms Braverman sent draft immigration policy to Tory backbencher Sir John Hayes from a personal email address, inadvertently also sending it to a staff member of another Conservative MP.
Ms Siddiq questioned whether the minister sharing "highly sensitive" information regarding "growth visas" could have been a breach under market abuse regulation.
She said the information could have affected Office for Budget Responsibility forecasts, saying "policy changes can constitute inside information".
"I believe this is a case to answer," the Labour MP wrote.
A spokesman for Ms Braverman, who has apologised for her "errors of judgment", declined to comment.
Ms Braverman - nicknamed ‘leaky Sue’ - resigned after she broke the ministerial code by sending a draft document to two people outside government, including one by accident. Yet Rishi Sunak rehired her as Home Secretary six days later.
It’s understood the document involved a ‘growth visa’ plan to raise ‘high-skilled’ immigration.
A person familiar with such matters told the Mirror last week that, if it had fallen into the wrong hands, it could have enabled “de facto insider trading”
This is because the scheme would have changed Office for Budget Responsibility forecasts on the deficit.
“You don't need to be a hedge fund to do that nowadays,” the person said. “It’s very easy to bet on Sterling movements from your phone.”
There is no suggestion the document was misused or passed on - and the person who received the e-mail by accident reported it.
But Shadow Chief Secretary to the Treasury Pat McFadden said: “We need urgent reassurances now that no market sensitive data was leaked.”
Ms Braverman - and later No10 - insisted there was nothing market sensitive in the draft document, although it had been intended to help the Office for Budget Responsibility draw up their economic forecasts.
"The draft WMS did not contain any information relating to national security, the intelligence agencies, cybersecurity or law enforcement," she said.
