“A number of buses have caught fire at a town centre transport depot. Heavy smoke drifted across Potters Bar after Hertfordshire crews were called to the scene on the High Street at 14:36 BST.”https://www.bbc.co.uk/news/uk-england-beds-bucks-herts-61543634
“Paul Kirby, a BBC reporter who saw the fire, said he spoke to bus drivers who told him they were relieved the underground diesel storage appeared to be safe. It is thought that up to seven hybrid buses had gone up in flames and “you could hear several loud bangs which they said were tyres” he said.”https://www.bbc.co.uk/news/uk-england-beds-bucks-herts-61543634
No idea, at this stage if the fire started in a battery; however, this quote also in the report: –https://www.bbc.co.uk/news/uk-england-beds-bucks-herts-61543634
“Eyewitness Shaun Cunningham said he heard an “unbelievable noise that sounded like a jet” and he saw a bus had “exploded into a ball of flames”.”
HT/Auto, Jim T, Jerome P and maybe others I’ve missed.