A pensioner has told a jury that a letter sent to Nicola Sturgeon threatening to blow up the Scottish Parliament had nothing to do with him.

Retired security guard John Mitchell, 76, from Tullibody, Clackmannanshire, was giving evidence at the trial of 43-year-old Joshua Rosenberg, from Kinfauns, Perthshire.

Rosenberg is accused of attempting to extort up to £95,000 from the landlords of the house he was renting in Strachan Crescent, Dollar, and then setting fire to it on February 20, 2015.

Prosecutors also allege Rosenberg sent a letter to Ms Sturgeon in February 2018 in a bid to blame Mr Mitchell for the house fire.

Mr Mitchell told prosecutor Alan Cameron he learned of the letter "when Special Branch came to my house".

The High Court in Glasgow heard that on March 29, 2015 Mr Mitchell went to Alloa Police Station and handed in a letter confessing to setting fire to the house.

Mr Mitchell told Mr Cameron: "I handed it in on the instructions of Joshua Rosenberg."

When asked why he had done this, he replied: "At first I refused to do it and he said he would improve the looks of my granddaughter."

The witness said he feared this was a threat to "disfigure her face" and added: "I feared for my granddaughter's safety."

Mr Mitchell, who denies setting fire to the house, added: "I was offered £150,000 by Joshua Rosenberg if I would take the blame. If I agreed to do time for him I would only get about three years because I was 72 at the time."

Rosenberg denies all the charges against him, which are alleged to have taken place between December 2014 and June 2018.

The High Court in Glasgow heard that the typed letter, which appeared to be signed by Mr Mitchell, arrived at the Scottish Parliament on February 20, 2018.

Addressed to Ms Sturgeon, the letter stated "When you receive this I will already be dead. And I give my life willingly to prove how I should not be forgotten.

"I will have detonated a pipe bomb with metal ball bearings, coins and my keys I made myself out of an old fire extinguisher.

"I'm going to take out the Scottish Parliament's main chamber tomorrow or the day after and I hope to take as many MSPs as I can with me to the grave."

The letter refers to him becoming "Scotland's first domestic terrorist" and ends with "Hail ISIS, hail Hitler, Hail Donald Trump."

The jury heard the note also contained a reference to Mr Mitchell coming to the High Court for Rosenberg's trial and stated: "I set fire to his house and I'm proud that I got away with it for years, I had great fun telling police that Joshua had threatened me to do it and had threatened my granddaughter."

Defence QC Gordon Jackson asked Mr Mitchell: "Are you suggesting someone else signed this," and he replied: "Somebody has copied my signature."

The court heard that Mr Mitchell stood for the Scottish Parliament in 2011 for the Scottish Homeland Party, who promised to "abolish multiculturalism at all costs". Rosenberg was his election agent.

The trial, before Lord Beckett, continues.