this sounds impractical for a small Cessna 152 to make a short direct journey from one aerodrome to another whilst in IMC where typical flying altitude is somewhere between 1500-6000ft.
You would fly a C152 in Class G, generally.
What are people's experiences of flying in IFR in IMC in Class G airspace in the UK?
It's done all the time. I did nearly an hour's worth this morning
No midairs in IMC in the UK, since WW2. In VMC, about 1 a year.
Is the LARS Deconfliction Service reliable/good, and how well do they provide separation?
It's OK when the weather is bad, but then almost nobody is flying. When the wx is good, they often don't provide a radar service; just a Basic Service "due to controller workload" (which is useless; you may as well be flying with a listening watch).
How does that compare with Victor airways in the US, which as far as I know, start at around 1200ft where you're given separation from other IFR flights by "Center"?
Play with the Eurocontrol routing tool (see other airways thread). I think IFR is pretty similar but in Europe one cannot generally go as low as in the USA. I think the US airways have their MEAs based on the higher of a) terrain i.e. MOCA and b) MRA, whereas most European airways have high bases seemingly unrelated to obstacles or navaid reception.
Based on the above, is it worth asking CAA/NATS to provide more direct, lower level Class E airways, which open up in non-icing conditions?
You could ask them but pigs will fly 100 years sooner
Here, ATC is privatised and nearly all of of GA pays no route charges, so they do the minimum legally required of them.
Yes it would be great to have the US-type (or French-type) Class E system...
But just departing VFR and drilling a long hole in the Class G clouds works fine. The sky is a very big place, and almost nobody in the UK flies in clouds. Also, most UK pilot forum readers think they get a nosebleed above 2000ft