109LWB:
We were told to ring 999 and ask if they had a unit pulling the vehicle over… don’t stop until you have confirmation. If the operator confirms, then pull over somewhere safe, if they don’t, well you can expect a few real police cars to be en route.
We also had signs in the windscreen to show, saying we won’t stop until it’s been confirmed.
This was for petrol tankers.
Not sure how it would work with dvsa though as they don’t have an easily rememberable number to ring.
DVSA will save you the job of contacting the police, they will do it for whoever refuses to follow/stop for them.