Note that I'm commenting on speed limits everywhere, not just the UK, it should be this Europe wide imho:
Schools and other "Pedestrian" areas - 20 mph ( though some of these ''zones'' are often in place nowhere near people living over here, old 30 zones messed up with speedbumps and other anti car **** and made 20... )
Road with Street Lamps (Speed Unmarked/built up area) - 30 mph, 40 mph at night like in Poland.
Single Carriage - 70 mph ( I mean these types of roads:
http://maps.google.nl/?ll=53.009321...d=I6Cdpv1UvpiJC1LNvp-csw&cbp=12,14.27,,0,5.32)
Dual lane Carriage - 80 mph ( I assume grade separated 2x2lanes or more, but without hard shoulders and rubbish deceleration/merging lanes etc)
Motorway - No limit, only locally, any limit makes 0 sense at night imho in many many places)
Countryside - 50 mph ( these types of roads, narrower single carriegeways:
http://maps.google.nl/?ll=51.985899...d=u_iJMawzABQe7ovzif8Ycw&cbp=12,43.42,,0,7.02 (used to be a 50 mph road, ruined with speedbumps and ''painted'' cycle lanes into a 40 mph road)
Obviously with local speed limits in danger spots, and probably about half the half the narrow ''countryside'' roads like these:
http://maps.google.nl/?ll=51.957344...=cUdgDEejSKv4RXcCFPXnZQ&cbp=12,47.48,,0,-1.52
So a tad higher than they are now

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Motorway and outside built up areas limits annoy me most especially at night.
What are these "limits" you speak of?
Fiscal recommended limits

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Holland is raising its NSL on motorways from 120 kph to 130 (80 mph) on 40% of its motorways in Sep

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Italy is experimenting with 150km/h in some places ( 93mph)
Poland recently went from 130 to 140 km/h limit.
Wish more countries would have the right idea.
There was a 160km/h limit experiment in Austria, unfortunately stopped. Also known for Greenpeace's and other eco morons their ''safety cars'' blocking the left lane at 130 km/h.
Ideally I'd see variable speed limits during daytime and no limit at night on motorways.