What appears to have happened with this is that someone took the passenger seat out and changed the sensor, which didn't help, so instead of taking it out a second time they just hacked it up, which obviously still didn't help.
The ebay listing for this car claimed that it had been worked on by someone called 'Audi Doctor', which several people thought was me. Said Audi Doctor works more to the Harold Shipman standards of care than my 'OEM+' approach
Witness this next heinous bodge:
Why is the driver's side belt tensioner not plugged in but not showing a fault code?
Oh, because someone has bypassed it with resistors
Mike came over today so we stripped the interior out. Quite a lot has to come out in order to get the airbag controller out, and then its fairly trivial to get the centre console out, at which point the carpet can be changed. Its so much easier to clean everything properly when its out of the car anyway.
All the wood trim will get polished while it's out
and all the leather cleaned up
Its been smoked in and smells quite bad so I've left the Aromatek running for a couple of hours to see if it helps. If not, I'll change the headlining.