You can choose not to advance into an intersection if it’s unsafe for you to do so, or to give way. That doesn’t necessarily mean the emergency vehicle has right of way.

Imagine a situation in which a driver was unaware of the presence of the emergency vehicle and advanced normally into an intersection, then was struck and injured by an ambulance driving under urgent duty driving conditions. If the ambulance had right of way, that injured driver would be held liable. That’s definitely not the case where I work.

Beacons ask other drivers to give up their own right of way. It doesn’t steal it from them.

Edit: I had a squizz at your Highway Code. It specifically does not say that the ambulance takes right of way:

>Rule 219

>Emergency and Incident Support vehicles. You should look and listen for ambulances, fire engines, police, doctors or other emergency vehicles using flashing blue, red or green lights and sirens or flashing headlights, or traffic officer and incident support vehicles using flashing amber lights. 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.