I always use "Halfords OAT" (used to be called Halfords Advanced) which is pink in colour. You can buy it either ready mixed or as a concentrate to mix with water yourself. If you look on Halfords and put in your registration number I suspect it will show you the one I mean. I don't believe it's suitable to mix with the blue antifreeze. I always drain out the old and start again with the OAT pink stuff.