Excellent writeup, a subject that continues to perplex on why cars have continued to be subject to ever increasing emission controls (all good of course) but the ever increasing need to reach out to others online in the first instance (those servers do suck up resources), or drive to an approved...
I would turn it off and leave the car outside in hot weather with all orifices open (boot/bonnet/doors) to let the moisture evaporate as much as possible
There was a claim of old still water stored in cars (often the container for windcreen washer fluid, a plastic pouch like a hospital drip)...
What tools do you have ?
A full sized spare wheel shoved under the front sill would be paramount.
Central London ?
Daylight so you don't end up getting stabbed.
I would go for a replacement TPS from personal experience.
Engine light goes out after three switch off/restarts (or immediately if you have the OBD2 thingy wired up)
Brake calipers, check the disc/pads are not overheating (rear left especially)
Earthing points and corrosion under the bonnet. Don't park/live near the coast.
If a saloon make sure you have a way of getting into the boot.
Get a spare key and always keep a replacement battery for it in the car...
I paid same for mine almost ten years ago with 150k on the clock and it still has all gears
Saloon or Tourer ?
Condition of the bodywork ? Modifications (wheels/brakes/suspension)?
Number of previous owners ?
Are you likely to be using it in a ULEZ zone ?
I recall during my time searching for a replacement modulator, one of the companies repairing them confirmed they did not dismantle the box fully but fitted parts on the outside which may or may not have been a third party switch.
Did you take pictures of the original modulator whilst checking...
If not a Honda workshop or trained mechanic, the garage might spend a bit of additional time and effort nailing down the exact fix.
If you check my early posts I changed a couple of sensors before replacing the modulator,. I had looked at sending it away for repair but fortunately found a...
Since you have mentioned the marque, was it a Honda garage that you took it to ?
If not, was the mechanic that worked on the car trained at a Honda workshop ?