Tory MSP Murdo Fraser has suggested the SNP's media chief is a Unionist sleeper agent in a bizarre tweet earlier today. 

The tweet suggested MI5 had used "dark money" to install Murray Foote – the former editor of the Daily Record and current SNP head of media – as a sleeper agent in the SNP. 

It follows a long history of suspicion that MI5 has a watchful eye on the SNP party, with a number of senior SNP politicians on lists for scrutiny as far back as the 1970s.

READ MORE: SNP leader was spied on by British state, documents reveal

In 2013, then-MSP Margo MacDonald wrote to MI5 chief Andrew Parker saying she believed some of the secret agency's staff were deployed in undercover operations in Scotland. 

She told him to use his staff to protect "against threats to national security" and not interfere in the upcoming Scottish independence referendum.