[UVB-76]

Average speed cameras are actually quite scary. In the UK they have only been used (as far as I'm aware) to enforce temporary speed limit reductions, most typically during roadworks, then removed once the speed limit is returned to normal.

In theory they could be deployed across the motorway network with ease, and overnight force people to abide by the maximum speed limits (which a majority of people do not currently do) or face fines and points on their licence (ultimately leading to a ban)

[timthorn]

No, they're deployed as regular speed cameras too. The M25 cameras are linked to a variable speed limit system to dynamically manage traffic flow; not sure if that fits in your definition of temporary (the cameras are permanent but the threshold speed changes) but there are also many instances of fixed speed cameras both on the trunk road network (eg the A14 near Cambridge) and even in villages (eg in Nottinghamshire)