Which vehicle will use a blue flashing beacon?
Emergency vehicles use blue flashing lights. If you see or hear one, move out of its way as soon as it’s safe and legal to do so.
Vehicles with blue flashing becons
All drivers should know what to do when a vehicle with blue flashing becons is approaching. Rule 219 of the UK Highway Code states the following about these types of vehicles:
When one approaches do not panic. Consider the route of such a vehicle and take appropriate action to let it pass, while complying with all traffic signs. If necessary, pull to the side of the road and stop, but try to avoid stopping before the brow of a hill, a bend or narrow section of road. Do not endanger yourself, other road users or pedestrians and avoid mounting the kerb. Do not brake harshly on approach to a junction or roundabout, as a following vehicle may not have the same view as you.
The UK Emergency Vehicles website goes into this in greater detail on this subject.