Joseph Mifsud allegedly told the Trump campaign about “dirt” on Hillary Clinton

A missing Stirling University academic whose links to Russia are being investigated by US authorities is a western intelligence operator, his lawyer claims.

There are renewed fears for the wellbeing of Joseph Mifsud, who allegedly alerted Donald Trump’s election campaign to Russian-held emails containing “dirt” on his rival Hillary Clinton.

The claim, which Mr Mifsud denies, prompted an investigation led by Robert Mueller, a former FBI director.

Stephan Roh, the Swiss lawyer who says he acts for Mr Mifsud, told The Times that the academic was a “western intelligence operator and did not act on behalf of Russia”. He would not elaborate.

Mr Mifsud’s background is shrouded in secrecy. Mr Mueller redacted some of the professor’s contacts and stonewalled Republican congressmen who asked if Mr