This risk is increasing with the proliferation of ANPR
So if picked up on ANPR with no road tax automatic penalty
ANPR is great but after a "ping" it still needs a real live Police Officer to stop the vehicle and speak to the driver.
ANPR all over the country "ping" on a constant basis but are rarely acted on.
Police no longer deal with No excise licence.
There are non Police vehicles fitted with ANPR that are solely around to detect vehicles with no excise licence. They just issue tickets to the last known keeper. There are very few of these vehicles.
Insuring a vehicle with no MOT normally invalidates Insurance with the insurance company. Not all companies check for MOT and just rely on self validation.
ANPR picking up just no MOT on its own will rarely be acted on.