MSPs have been placed on terror alert after a string of suspicious packages containing white powder were sent to Scottish politicians' offices.

The SNP's headquarters were targeted along with the office of one of the party's MPs, and the municipal buildings of an SNP-run council.

Becky Thomson, head of security at the Scottish Parliament, said all of the packages were were associated with the forthcoming UK general election.

Each is though to have contained come form of chemical crystals, which is being analysed by police.

Officers were also last night investigating suspicious packages sent to the Scottish Police Federation building in Glasgow and to the Association of Scottish 

Police Superintendents based at the Scottish Police College, Tulliallan, Fife.

A package containing white powder was sent to SNP MP John Nicolson's constituency office in Kirkintilloch on Tuesday, which sparked a response from emergency services.

It was initially claimed the letter contained a biscuit, but Mr Nicolson later confirmed it was a chemical substance.

On Wednesday a similar delivery was made to Angus Council in Forfar. It was reported that the package contained a note saying ‘Get SNP out. Tories in’.

It has now emerged that a third package was sent to the SNP HQ in Edinburgh during the past two days.

Police Scotland and have now issued safety guidance to MSPs in the wake of the incidents, with specific instructions on how to handle letters containing white powder - which has been used to deliver Anthrax spores. 

Ms Thomson said: "The security office would like to remind all members and their staff of the main actions to take if suspicious mail is received at a local office: rest the package on a flat surface, make no further attempt to open the package, or touch or move it, call 999 immediately and evacuate the area.

"We aim to deliver a training session with Police Scotland colleagues on mail handling, suspicious packages and 'white powder' as soon as possible."

Politicians have been on high alert following the terrorist attack on Westminster last month, which saw Khalid Masood gunned down by armed officers.

It has emerged that in the days after the attack a hoax letter containing white powder was sent to Moray MP Angus Robertson's constituency.

The package, which originated in Lancashire, was posted to a Keith pub, allegedly from "the UK IS support group".

Police Scotland Assistant Chief Constable Wayne Mawson said that the letter sent to Tulliallan did not contain a noxious substance.

He added: "Enquiries continue at the other incident in Glasgow. At this time there are no apparent injuries to any officers or staff as a result of these incidents.”