from what I can tell, that is the accessory belt tensioner, and it is supposed to move as the load on the engine changes, but not like it does at the moment.
I think it will require a replacement tensioner, (and belt) https://ford.7zap.com/en/car/48/no/1...2/66954/#6A247
Thank you ! That makes sense. Right, need to call Arnold Clark in the morning to see if its covered under their warranty.