Got tickets for Wolfmother next week and it
seems the carpark is already full. (Don’t know why,
Idigo2 isn’t that big and I don’t think anything else is on
that day) Anyway, what alternative parking is there? I’m coming up
from Ashford in Kent.

Ashford International Station?

There is a b “n” q and cinema just off the A2 roundabout exit for o2, huge caspark but check to make sure it’s not “customers only” I’ve never checked.

IIRC, the O2 car park was made deliberately small, to encourage visitors to use public transport. Travelling from Wiltshire, via the M4, I’d be nuts to try to drive there, but I gave up driving around London to park close to music venues years ago. On-street restrictions, and lack of easily accessed car parks mean its easier to use the Toob. Even for the O2, parking at Hammersmith and using the tube and DLR is a doddle, and getting away is dead easy. I’d find somewhere out around Lewisham, perhaps, and get the DLR, or one of the surface rail trains that connect.
I have horrible memories of going to Wembly for an American Football game, and spending nearly two hours in the car afterwards just trying to get out of the poxy car park.

Park at the O2 station car park. It’s literally next door to the official O2 car park and it’s about a third of the price and usually half empty. It’s just a pay and display and you can pay with a card.