Just for the record seeing that no one replied I bought a refill kit from Halfords and recharged the system for £40 which included the anti bacterial bomb . System now works great . I was quoted £120 by my local Dealer ???
If your system losses coolent again, check the aircon heat exchanger, there are 2 lugs, left and right at the bottem where it mounts, they always fail there due to corrosion, when dirt/salt collect. Usually there's a U.V flourecent diy in the coolent refils so you should see the leak if you have a uv light.
I cleaned mine up wound 2 layers of nylon thread, soaking each with cyano-acrylate (super glue), and another coat to finish worked a treat, still going 2 yrs later when i sold the car. Much to the surprise of a masterfit (vauxhall) technician who lived nex door!