Thanks mate. Decided not to do it as an oil change seems to have fixed the issue for now. I dont get the rattle anymore even if the car has been sat for long. Will definitely look into it if the noise comes backthe chain tensioner is easy to replace and costs £45 for an INA brand one which is OE quality
prime the tension in fresh oil before fitting it - A6510500800 this is the part number
fitting takes about 30minutes- just make sure the engine is at TDC otherwise takes some brute force to push it in =)