Good News, the dealer (Jason Mazda in Osborne Park) replaced the battery for me this morning and the HDC fault has gone. The guy tested the old battery and said there was only 400CCA left on it and it was deffo on it's last legs..
The car was sent to a specialised Jag/LandRover service centre yesterday and they cleared the codes and sent it back to Jason Mazda saying it was fixed. The guy who sold me the car rang back later in the day and said they hadn't fixed it and it would need to go back. I told them it's probably just the battery (after reading up on here and disco.co.uk) and also spoke to helpful guy at Franzone Motors who also confirmed my suspicions. Jason Mazda agreed to send someone out and replace the battery under warranty this morning. Great service from them so kudos to Scott at Mazda. Not so much to the Jag/Land Rover 'specialist' (who shall remain nameless) in Osborne Park...All in all very satisfied.

