The force said the alleged incident reportedly took place in 2017 and "enquiries are at an early stage".

Mr Linden stepped down as North Lanarkshire Council leader last July amid an accusation of sexual harassment. His resignation led to the collapse of his party's administration, with Scottish Labour regaining control of the local authority.

Mr Linden then quit the council and the SNP in March amid fresh claims of misconduct.

At the time, Mr Linden said he refuted the allegations and vowed to "robustly" defend himself.

The Sunday Mail reported at the weekend that five men have made allegations, with two speaking to detectives. Mr Linden told the newspaper he did not accept the claims made against him.

Police Scotland said it is currently investigating a single complaint.

A force spokesperson said: "Officers are investigating a report of a sexual assault incident having taken place in 2017. Enquiries are at an early stage and ongoing."

Several councillors have since left the SNP's group in North Lanarkshire to sit as independents.

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On Saturday, SNP leader and First Minister Humza Yousaf was campaigning in Bellshill ahead of a by-election triggered by Mr Linden's resignation from the council.

He said the party would investigate how it handled complaints regarding Mr Linden and admitted the SNP's issues in the area "could have been handled better".

Mr Yousaf said: "We're absolutely holding our hands up. I, as first minister and leader of the party, say that things of course could have been handled better.

"That's why we'll do the investigation."