Graeme wrote:
Well, I think the battery itself is OK. Went for a run Thursday
afternoon to charge the battery, then left it until this morning
(Tuesday) with the earth lead disconnected. Reconnected and an easy
start, from what felt like a still fully charged battery.

To recap, if parked with the battery connected, the battery is almost
flat after 48 hours, as in not enough to turn the engine to start. The
courtesy light switch(es) were suspect, but same thing happens
with them disconnected.

I tried Harry's bulb trick again (small MES panel light bulb between
-ve battery terminal and earth strap), and nothing. Tried using an
ammeter. Nothing. Yet current must be flowing somewhere.

Can't really help, but an online friend had a similar problem. AA said
battery. Halfords thought the same but did not try to sell him a new
battery.............. hmmm.
It seems that stuff can come apart in a battery and flatten it. I did not
know this.
He bit the bullet, bought a new battery and all has been fine for weeks.