I have a very encouraging update !
even though the car is under extended warranty - as you all know batteries are not covered and I would probably be pushing my luck to ask for a replacement of the battery I had (which was replaced less than 2 years ago), to take it into my dealer ship would have encountered charges for diagnosis, and probably a new battery at their rates... alternatives were the new Bosch Silver Plus battery as previously mentioned by other forum members (about £122 from halfords but you get a free toolkit if you order online).
So I decided to bite the bullet and try and fix it myself - I bought a new battery charger, A Ring, Powerring smart battery charger (8 Amp) from my local halfords last night, got it home and took out the battery and hooked it up on the kitchen worksurface (as you do). First pass said it had no amps and about 3v in it, first charge run said the battery was broken and needed replacing.
However, this particular charger has a special deep reconditioning function for knackered / old batteries - so I thought "nothing to lose" and went for that. That spent the best part of the entire night running and just before leaving for work this morning, it finished the reconditioning cycle and switched to charging - So I left for work (in the other 1/2's 1 series) and came back this evening to find the battery completely juiced up and the charging cycle complete.
I have just put it back in the car, alarm went off (as you would expect), and I had to reset the clock and the time but that was it. I did notice that the radio came on as soon as I fired her up - so maybe this is where the bug/drain is ??? who knows. Anyway, everything is working and I had no issues with the clickety click behind the console - it seems to be working just like a fresh new battery without issues - so far so good.
here is the link to that charger with the reconditioning function - it was 50 something quid but has saved me probably over 200, plus allowed me to keep my OEM battery (and not kill my warranty probably).
http://www.halfords.com/webapp/wcs/..._productId_532907_langId_-1_categoryId_165629
worth every penny I think as it goes that extra mile to recondition a battery that I would have otherwise replaced.