Scotland's ruling party faced fresh turmoil Wednesday after the husband of its former leader Nicola Sturgeon was arrested as part of a police investigation into financial irregularities.

Peter Murrell, 58, was chief executive of the Scottish National Party (SNP) for nearly 25 years until he quit last month.

In a statement, Police Scotland said they had taken a 58-year-old man into custody for questioning over the SNP's "funding and finances".

"Officers are also carrying out searches at a number of addresses as part of the investigation," the police force said, without naming the man.

Police were seen outside the Glasgow home of Murrell and Sturgeon, and at SNP headquarters in Edinburgh.

UK media identified the arrested man as Murrell, who has long faced questions over the alleged disappearance of £600,000 (€683,040) in SNP donations that were meant to support its drive for Scottish independence.

He also failed to declare a personal loan of more than £100,000 that he gave to the party.

Murrell resigned from his SNP leadership post after the party falsely denied to media that it had lost 30,000 members. 

"While there was no intent to mislead, I accept that this has been the outcome," he said in resigning.

The revelation about the membership numbers came as the SNP held a bitter election to replace Sturgeon as leader and first minister.

After more than eight years at the helm, Sturgeon said in February that she lacked the "energy" to carry on and was stepping down.

But she also remained dogged at the time by the police investigation into her husband.

There was no immediate comment from Sturgeon, who was succeeded in late March as party leader and first minister by Humza Yousaf.

The SNP said in a statement that it "would not be appropriate to comment on any live police investigation", but said it was "cooperating fully" with the police.

The arrest plunges the SNP deeper into crisis with Yousaf already accused of snubbing his defeated rivals for cabinet posts after the bad-tempered leadership campaign.

The campaign exposed fault-lines over the party's future direction, after its demands for a fresh referendum on Scottish independence were blocked by the UK government and Supreme Court.

"This is a deeply concerning development and the Police Scotland investigation must be allowed to proceed without interference," said Jackie Baillie, Scottish deputy leader of the opposition Labour party.

"We need Humza Yousaf and Nicola Sturgeon to urgently state what they knew and when," she added.