Police Scotland has spent more than half a million pounds on staffing costs for Operation Branchform since the investigation was set-up almost two years ago.
A dedicated team of detectives is investigating how the SNP spent donations intended for a second independence referendum campaign.
It has led to three senior Nationalists - including Nicola Sturgeon - being quizzed by cops before being later released without charge.
A Freedom of Information request showed Police Scotland had spent an estimated £43,981.03 on overtime costs in connection with the investigation – on top of an estimated £551,662.53 on salary costs up to the end of March this year.
Details of the FOI request were first reported in The National.
Operation Branchform was launched in July 2021 after several members of the public made complaints to the police regarding SNP finances.
Iain Livingstone, who will soon retire as Chief Constable of Police Scotland, insisted last month that Operation Branchform was being conducted with “integrity”.
In his first public comments on the investigation, the top cop added: “Police investigations must be allowed to progress without any form of political interference.”
The investigation has rocked the world of Scottish politics and overshadowed Humza Yousaf's first months in office since he succeeded Nicola Sturgeon as SNP leader.
Livingstone said: "Under Operation Branchform, a dedicated team of officers from Police Scotland’s specialist crime division continue their investigation into the funding and finances of the Scottish National Party.
“A diligent, thorough and proportionate criminal inquiry is being conducted with integrity.
“Two individuals have been arrested and subsequently released without charge, pending further investigation, investigations which continue.”
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