Get the stories that matter to you sent straight to your inbox with our daily newsletter.Shamed SNP politician Derek Mackay has finally quit the party in which he was elected to represent Renfrewshire North and West.He has resigned ahead of May’s Holyrood elections after more than a year of snubbing the parliament and trousering his meaty pay packet.Scotland’s former finance secretary leaves the SNP following his suspension from membership last February.The party say his quitting means