SCOTLAND’S politicians were put on terror alert yesterday after the SNP and the Scottish police became further targets for hate attacks by mail.

Following the delivery of suspicious packages on Monday and Tuesday to the offices used by the SNP, a third package was sent to the party’s headquarters in Edinburgh yesterday.

In addition, Police Scotland confirmed last night that two more packages had been intercepted at the Scottish Police Federation’s offices in Glasgow and the Association of Police Superintendents in Tulliallan, Fife.

Yesterday, Police Scotland said they were writing to every elected representative in Scotland warning of the prospect of packages and explaining in detail how they should be dealt with.

The first package arrived on Tuesday at the Kirkintilloch office of East Dunbartonshire SNP MP John Nicolson, with the second arriving on Wednesday at Angus Council offices in Forfar used by the SNP. The latter was reported to contain a note saying: “Get SNP out. Tories in.”

It was reported that the items sent to the SNP venues had contained “white powder” in what appeared to be the threat of an anthrax attack similar to that carried out in the USA in 2001.

Though Police Scotland took all the incidents seriously and deployed fire and rescue teams as well as trained officers, all five packages were cleared of containing any dangerous substances, leading to speculation about a hoaxer at work.

The Scottish Parliament’s security management decided to alert all MSPs directly and issued the following warning: “Between Tuesday, April 25, and Wednesday, April 26, three suspicious mail packages containing a white powder type substance were sent to an elected official, a political party headquarters, and a council building.

“All packages were associated with the forthcoming UK General Election. Police Scotland’s enquiries into this matter are ongoing. We enclose a letter from Police Scotland with some further advice regarding mail handling, suspicious packages and indicators of white powder. We would be grateful if you would take the time to review this information and discuss with your local office staff.

“The same information has been issued to all elected representatives across Scotland.”

The security manger added: “We aim to deliver a training session with Police Scotland colleagues on mail handling, suspicious packages and white powder as soon as possible. We will provide you with further information on this shortly.”

SNP sources were playing down the incidents yesterday, and it is believed that police advice is not to highlight the matter in case of copycat attacks. In London yesterday, a 27-year-old man was detained in an “intelligence led” police operation in Whitehall not far from Downing Street. The man was found to be carrying knives when he was pounced on by police officers. He was reported to be a British passport holder.

Just five weeks after Khalid Masood killed a police officer and four passers-by before he was shot dead, Westminster was on high alert but it appears that the suspect was tracked by counter-terrorism officers before he came near Parliament and Downing Street.

After the London incident, a police statement said: “The man was arrested on suspicion of possession of an offensive weapon and on suspicion of the commission, preparation and instigation of acts of terrorism. Knives have been recovered from him.

“Detectives from the counter-terrorism command are continuing their investigation and, as a result of this arrest, there is no immediate known threat.”

Last night Labour peer Lord Peter Hain, the prominent gay rights and anti-apartheid campaigner, was also revealed to have been a target for a “white powder letter” which was intercepted before it could reach him.