Following Keefy*2010 and Plasma'screen advice I took it to a reputable local garage that has all the top gear. 45 minutes later whilst on my hands and knees I was shown (with the aid of an ultraviolet lamp) the damaged area of the condenser radiator where the leak is. It's booked in next Thursday for a new condenser radiator to be fitted. Cost is a reasonable £200 plus a further £45 to have it regassed.