It was pointed out that Y and Z flight plans are legally required for all airways departures and arrivals from airfields in the restricted zone which do not have an approved approach proceedure.
In the UK, Y and Z never normally need to be used, because (unlike say Germany) UK allows "I" flight plans to/from non-IAP airfields.
However, the severe IFR slot system imposed during the olympic saga (typ. 1 or 2 IFR slots per hour) will mean the slots will be grabbed quickly by those who get in first, and any subsequent traffic will have to travel VFR.
Which is OK if you are hacking around UK Class G, or popping over to N France etc. But let's say you want to fly to Croatia and everybody has grabbed the slots at your airfield
Logically, a Z flight plan, with a changeover at say KONAN, would do it perfectly. But these are (according to the ATCO I spoke to, who ought to know what he has been told to operate) to be banned.
So the only way will be a V FP to say LFAT, and an I FP from there onwards.
On top of that we seem to have a confusion on whether the IFR slots are for any IFR flight (including e.g. IR training flights going to bang a local Class D ILS) or just for flights into London Control airspace.
The text on that has recently changed (see thread on this recently) and it appears to be the latter, which is much more sensible.
Adam whilst a single land based radar may be incapable of providing an accurate height read out
ATC radar doesn't give any height data. Neither does any "PPI" radar including military. Only the more complex military radars (probably all phased array nowadays) can give you height info.