100mph or more is extremely appropriate! It's nothing in a modern car.
It absolutely is not, primarily because of the consequences of a collision, but also because others on the road may not have the skill or reactions to deal with you going that fast. You might not even do anything wrong - it could be a totally unexpected mechanical failure caused by a totally unforeseeable manufacturing defect.
As you point out the main risk comes from speed differentials and I would not in principle be against a "delta" rebuttable presumption of guilt if passing another vehicle at significant differential (say 40mph) in the immediately adjacent lane.
Presumption of guilt is neither here nor there. We want people to stop dying on roads, not to decide who to blame when they do.
Reducing single carriageways to 50mph is a disgusting idea. Sadly your side will probably win as it's politically popular...
Many rural Councils are already doing it progressively with signage anyway. Doing it nationally would save them the cost, allowing it to be spent on other road safety matters or even public transport subsidy.
just shows why so many shouldn't have a licence.
It would be possible to have a system whereby the driving test was much, much more comprehansive and difficult and would include high level medical tests such as reactions tests, thus only allowing people on the road capable of driving at the kind of speeds you would like to see, as well as prohibiting cycling and bringing in jaywalking laws. However the roads are for safe transport for all, not for a personal race track for people who are (or think they are) capable of driving at very high speed, not to mention the environmental issue of the much higher energy consumption at high speeds.
Therefore, while I'd agree there are some who shouldn't be on the road at all, I would say this opinion is well wide of the mark, and you should simply book a track day (or make a visit to the Nuerburgring Nordschleife) when you want to drive at high speeds, and leave the rest of us to use the roads safely to reach our destinations, which is their purpose.
They should lose their licences and take the bus.
I think people who think it's appropriate to drive as fast as you are suggesting are the ones who should lose their licence and take the bus, as with the exception of professional racing drivers they almost universally have an elevated view of their own driving capability - and that arrogance is one of the most dangerous things that can be on the road. Fortunately, with the increased prevalence of enforcement, that's more likely than what you would like to see, unless they're very good at spotting yellow boxes.
I understand that the national speed limit replaced "end of restrictions" when Jaguar were found to be using the M1 as a test track. You could possibly justify 80mph on proper motorways, but speeds on single carriageway roads need to drop.
Totally agree.
How about:
Motorway with hard shoulder: 80mph, but 70mph in case of rain or fog
Motorway without hard shoulder or other dual carriageway: 70mph (or possibly 60, I could be sold on that, with signing up for specific motorway style dual carriageways like the North Wales Expressway).
Single carriageway: 50
Single carriageway without marked centreline: 40
Urban: 30 or 20, I struggle to decide which should be default to be honest. But too much signing up and down is unhelpful as it is distracting, so better to pick one of those and stick to it.
Aside from legally mandated limiters these limits would apply to all vehicles, so there would no longer be bus/van/lorry differentials, thus minimising overtaking on single carriageways which is incredibly dangerous.
The 10 suggestion is probably not sensible in many places, but I could see a sense in having Dutch style "Woonort"/"Auto te gast" zones where cyclists and pedestrians have absolute priority and the car is a guest and needs to drive at the lowest practical speed. In effect the whole thing is a big zebra crossing - kids can run out and drivers must stop, for example. This would only sensibly be within residential cul de sacs and the likes.