Which vehicle will use a blue flashing beacon?

Vehicles with blue flashing beacons

Rule 219 of the UK Highway Code states the following about what to do when a vehicle with blue flashing lights is approaching:

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.

If you don’t move out of the way of an emergency services vehicle such as an ambulance then you could be fined.

Only vehicles used for emergencies can have blue flashing lights fitted to them. The Suffolk Police website states:

Only emergency vehicles can display blue lights so it is an offence if your vehicle has any LED or neon under-vehicle lighting system or lights on windscreen, washer jets or number plates emitting a blue light.

The UK Emergency Vehicles website goes into greater detail on the use of blue lights.