In the UK we have "IFR" and we have "IFR".
The first one is on the IMC Rating and basically it is a "VFR" flight, with holes drilled in clouds when convenient. No CAS privileges over a VFR flight - still have to get a clearance for every one.
The second one is on a full IR and it is as per international IFR procedures. Here in the UK, mostly Class A.
Sure one could fly to LOS fully IFR but since the place has no IAP then what would happen is that when you get dropped out of CAS (dropped out by London Control) you continue a DIY descent and land VFR.
I don't think I have ever flown fully-IFR to any place down there but it may well be that London Control will hand you over to either Bournemouth or Southampton - both of these are CAS (Class D) which is continuously connected to London Control's Class A. So, I can imagine, one could get a "radar letdown" by B. or S. all the way down to their MVA which is probably about 2000ft.
As regards valid IFR routings, that's a whole big subject. Nowadays there is this
tool which works really well for most routes.
I rarely fly fully IFR around the UK because just drilling a hole in IMC in Class G is so much simpler. Not so in the winter though; one wants to climb up to VMC on top, and that usually needs an IR.