Mr Beattie, 71, has been arrested and is being questioned by officers from Police Scotland.
According to a police spokesman, the arrest was made in conjunction with the continuing investigation into the SNP’s fundraising and finances.
According to him, a report will be filed to the Crown Office and the Procurator Fiscal Service.
Mr Beattie represents the Midlothian North and Musselburgh constituency in the Scottish Parliament. He was the SNP’s treasurer for 16 years before being beaten in an internal election in 2020 by Douglas Chapman, but he returned to the position when Mr Chapman resigned a year later.
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