[ThomasG]

I think I've found it, I'll test in the evening.

Now for the hard part:

Emergency corridors rely on drivers making as much space, the corridor as wide, as possible. To achieve it, cars need to partially at least leave their running lanes.

For that to be possible, such a behaviour would have to be listed in highway code, and that's not likely to happen soon.

Therefore, what I would propose instead, as intermediate measure, is:

Whenever congestion on any kind of motorway or dual lane carriageway causes traffic to stop, ALL drivers are to position themselves:
Drivers in right-most lane- with right wheels on the white solid line, but not beyond, and with at least 4metres of open space from car ahead
Drivers in all other lanes- with left wheels directly next to left broken or solid line that denotes lane division. Passenger cars and small vans to leave at least 4metres if space ahead, bigger vehicles to leave enough space to perform complete lane change with end positioning of vehicle completely parallel to lane.

This, should allow to:
A) stay within regulations if highway code if there is no accident ahead , just a clogged up carriageway

B) allow to further widen the corridor if there is emergency vehicle approaching.

Drivers are to remain "wide" after emergency vehicle passed, as there may be more of these to follow.