The DVSA and certain traffic officers (HETOS) have powers for stopping vehicles. They can force you to stop on trunk roads and motorways in England and Wales.
VEHICLE STOPPING PROCEDURE: Officers from the Driver and Vehicle Standards Agency can legally stop any vehicle on all roads in England and Wales.
Rule 107: DVSA Officers may attract your attention by flashing amber lights from in front of your vehicle.
They can also request you to follow them to a safe place to stop. They might make a signal from behind your car directing you to pull over to the side of the road.
As a rule, they will point and use their left indicator as a gesture for you to pull over and stop. Motorists MUST obey any signals given by authorized persons. It is a motoring offence not to comply with their directions.
Rule 108: In England, uniformed traffic officers also have powers to stop vehicles on some 'A' class roads and the majority of motorways. The most likely reason for getting stopped by a traffic officer is on safety grounds. For example if your vehicle has an insecure load.
In most cases, they will attract your attention by flashing amber lights. They do it from behind your vehicle or they might direct you to pull over to the side. In this case, they will use a pointing signal and use their left indicator ahead of your vehicle.
If you get directed to pull over, you MUST do so and stop your vehicle as soon as it is safe and then switch off your engine. Failing to comply with signaling directions of authorized persons is a traffic violation.
Rule 109: Road users MUST obey all traffic light signals and all traffic signs giving orders. This includes any temporary signals and signs.
Rule 110: Drivers and riders should only flash headlights as signals to other road users to let them know that you are there.
The United Kingdom Highway Code laws do not allow you to flash your headlights to convey any other message. You must not use vehicle lights to intimidate other road users.
Rule 111: Likewise, you should never assume that someone flashing their headlights is a signal inviting you to proceed. Instead, use prudent judgment and proceed with caution.
Rule 112: Motorists MUST NOT use the vehicle horn:
You should only use the horn while your vehicle is moving. This only applies if you need to warn other road users of your presence. Horns should never be sounded aggressively!
Highway Code Stopping Procedures in the United Kingdom