Surely if tax/mot/insurance all on line, then computer can issue the fines for that side of things

Cameras only really pick up SORN offenders beyond the above, as a breach/abuse of SORN has to be witnessed... the rest is online/automatic.
Where Jason etc come into it is if cars are that are non compliant come to their attention ie at accidents/traffic stops/investigation of other illicit activity

When a car is sold, it should be the sellers responsibility to go online and submit the purchasers details, if licensed trader include the trade plate numbers. The seller then declares the car SORNed/Sold, gets refunded any remaining tax (to the day) Car is instantly transfered to the buyer and becomes SORNed until the buyer taxes and insures it.
The V5 reference numbers would allow this to be done (relatively) securely. The completed V5 could then be sent off as it is now, according to whether the purchaser is trade or private. If the details submitted online don't tally with the details on the posted/signed V5, then the buyer is the one responsible for the discrepancy...
Simples
