I'm still learning my way around the bike mechanical side! I think the chain currently is too loose. It was in need of oiling begore it went in for mot. I think it could have been too loose then mixed with chain lube and popped off ?

I am in Trowbridge. Got Wednesday off so will give it a good look over and do a visual inspection. Fingers crossed it'll be somthing simples! Keep you posted once I've opened her up !