An investigation is under way after a fire near the offices of the Sunday Herald linked to the loyalist disturbances in Glasgow on Friday night destroyed an electricity substation.

CCTV footage shows two men approach the seven-feet tall metal generator in Renfrew Court adjacent to the Flying Duck basement club, frequented by students, and the Atholl Arms bar shortly before 11pm.

They disappear behind the substation and 10 minutes later flames can be seen at the base of the generator. The men, who were wearing dark trousers and waist-length hooded jackets, then emerge and stand nearby. Each of them light a cigarette. At this stage at least one of them has also changed his jacket from a pale-coloured top to a darker one.

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One of the men had sunglasses on his head and the other was carrying a rucksack. They both appear to be looking down at their hands and, as the blaze takes hold, they make off in the direction of Renfield Street.

Dozens of people fled flats above the club when flames reached as high as four storeys.

The incident came at the same time as loyalists caused ugly and violent scenes across the city centre.

Nasser Aldejhil, 32, a student who lives on the fourth floor of the building adjacent to the Newsquest Herald & Times offices with his wife and daughter, said: "I heard people shouting 'fire, fire, fire'. I looked out and the flames were outside the window. I panicked and woke my wife and daughter and we ran to the street. It was terrifying."

Police Scotland last night said a full investigation was under way into the fire-raising incident as part of the overall investigation into Friday night's disorder.