So I put the old Bosch battery on charge yesterday and still no joy today, I did however notice when I was looking round that the interior lights seemed to have been set to being permanently on. I'm guessing this might have happened last week when I first encountered the problem & I was out there in the dark, so over the course of a week they could well have tipped an already on its way out battery over the edge.
The old battery is showing as fully charged but I've no way to test if it's got bad cells I'm just guessing, I'm hoping Euro carparts up the road is open so I can try a more powerful battery in it. Fingers crossed that's the problem