Now I may be wrong here, but this is my recollection of the events.
Ray Peake who owned the place when it was Callums, had the mural done by students at the College in Sandy Lane....but I don't think he applied for planning permission...he was told it had to come down......but then he sold up....so it wasn't taken down completely....I think the bit that is missing fell off.
I'm sure there was a bit of an outcry when he was told it had to come down.......think the picture represents the town of Accrington, and he felt that it should remain as it was an interesting bit of art.
Now I will wait for those with better memories to come and and tell me where I got it all wrong