Peter Murrell, 58, is being questioned after being taken into police custody on Wednesday morning.

Police Scotland said officers were carrying out searches at a number of addresses as part of the investigation.

Mr Murrell resigned as the party's chief executive last month, a post he had held since 1999.

He has been married to Ms Sturgeon since 2010.

Ms Sturgeon stood down as first minister last month and was last week succeeded by Humza Yousaf.

There is currently police activity at the couple's home in Glasgow and at SNP headquarters in Edinburgh.

There are 10 uniformed officers stationed outside the former first minister's home, alongside one police vehicle and an incident tent in the front garden.

The curtains and blinds remained drawn and there was no sign of anyone in the property.

Meanwhile, two police officers were posted outside SNP HQ and there were other officers inside.

At least six marked police vehicles were parked outside the building.

An SNP spokesperson said: "Clearly it would not be appropriate to comment on any live police investigation but the SNP have been cooperating fully with this investigation and will continue to do so.

"At its meeting on Saturday, the governing body of the SNP, the NEC, agreed to a review of governance and transparency - that will be taken forward in the coming weeks."