Police have arrested Nicola Sturgeon, Scotland’s former first minister, as part of an investigation into the finances of the governing Scottish National party.

The arrest on Sunday marks a major escalation in a police probe that has plunged the pro-independence SNP into an unprecedented crisis. Sturgeon, who formally resigned as party leader and first minister in March, is the third person to be arrested in connection with the investigation.

The party’s former chief executive, Peter Murrell, who is also Sturgeon’s husband, and its then treasurer, Colin Beattie, were arrested in April and released pending further investigation.

Police Scotland, the national force, said it had arrested a 52-year-old woman on Sunday in connection with the ongoing investigation and the person was being questioned by detectives. A person familiar with the situation confirmed that the arrested person was Sturgeon.

Police have been investigating the SNP since 2021 after receiving complaints related to donations made to the party to fight a future independence referendum.