For heavens sake... They would never try and pursue this in the Scottish courts. It would cost them ten times more than they could ever hope to recover, assuming they were not so intellectually malnourished to even try in the first place.
They are claiming Keeper liability which is impossible in Scotland, for now. They have no idea who the driver is and that is the only party they can pursue in Scotland, even if they were stupid enough to even try, which I'd place a £100 bet one will never happen.
They are hoping you are low-hanging fruit on the gullible tree and will pay up out of ignorance and fear.
You can just ignore the PCN and all subsequent useless debt recovery demands. Debt collectors are powerless to do any thing except to hope to pluck the ripe fruit off the gullible tree. No claim will be forthcoming, especially for anything less than about £1,000 or more.
If the Keeper is a company, then even better. A company cannot have been the driver, no matter how moronic the parking company tries to be.
If the alleged contravention occurred in Scotland or the Keeper is resident in Scotland, nothing can happen.
An English company trying to sue a company, not an individual, in the Scottish courts under the Simple Procedure would never happen and I am prepared to accept any bets on this. Just ignore it and it will eventually go away.