I phoned the Solent ATC on the number here local copy (note this leaflet is more than 10 years old) and presented to him my scenario in post #1.
It turns out I was right i.e. there would be a bust at the point shown, unless Solent manage to get a handover to Gatwick which owns the next bit, and this is apparently something that happens very rarely.
While Solent has no responsibility for ensuring CAS isn’t busted further on, they would either do the above mentioned (rare) handover to Gatwick, or they would notify the pilot that the base of CAS in x miles is 5500ft.
They can also offer him a heading change to the south east where the base of a bit of Class A is FL065 and there one can fly (for a bit) at FL064. I was actually offered this too, on that flight, but it helps only a little.
So it looks like a CAS bust is unlikely in practice. However it seems to me that if they were really busy with their own traffic (which does happen) they might forget and leave you with little or no time to descend, and then it would be your responsibility.
BTW Solent own the Class A above their Class D up to FL070.
So in the scenario where the controller is very busy and you have to make either a rapid descent or a few orbits to descend at a better pace, what about being under “radar control” and trying to get permission on an exceptionally busy frequency? I had this a few weeks ago with Solent and the controller (when we could speak) was absolutely understanding and no issues.
I can see a tricky situation arising because under radar control you cannot change altitude or heading.
Strictly speaking, you cannot avoid the unathorised entry into Gatwick airspace, in what is de facto a lost comms situation.
Surely you either have a clearance into CAS with a clearance limit or one to the limit of CAS if no limit is provided. If you reach the boundary of London and Scottish control without onward clearance do you hold until one is passed? In the case of an abbreviated flight plan, filed to cross CAS in flight, it may be as well to tie down the clearance limit, but as a pilot you cannot be expected to know the intricacies of who controls a given block of airspace.
I agree with Giles. Unless they gave you a clearance limit it is their problem to sort the handover.
I agree with both of you 
In the absence of ATC instructions, assuming that forward coordination has taken place is the only meaningful option in IFR in CAS.
The pilot might still get a load of hassle though, afterwards, with the CAA.
What would be the “hassle” if you follow the regs in IFR? What could they criticize? The above suggestion by Jason and Gilles would be the assumption for a non-UK pilot coming from the continent, and seems to me to me to be SOP. Anyone able to quote a regulation to the contrary? If a clearance given without a corresponding clearance limit, then the limit would be the last one received. In most many/most places (not in France) this would be the original “cleared to XXXX (destination) via …”
In most many/most places (not in France) this would be the original “cleared to XXXX (destination) via
Yeah, but we all know that phrase – probably old as IFR itself – means nothing if any of the flight is OCAS, or any of the flight is in the UK 
In fact the current CAA terminology manual (posted here the other day) specifically says the UK must not use that phrase.
would be the assumption for a non-UK pilot coming from the continent,
He would probably get away with it
chflyer wrote:
The above suggestion by Jason and Gilles would be the assumption for a non-UK pilot coming from the continent, and seems to me to me to be SOP.
Forget about non-UK, we are borh UK pilots. If I am in controlled airspace on an IFR flight plan, the controller is responsible. Peter, I think whoever you spoke to in Southampton is wrong.
Peter wrote:
Yeah, but we all know that phrase – probably old as IFR itself – means nothing if any of the flight is OCAS, or any of the flight is in the UK
I have never flown in the UK but I have seen many threads with this claim that an IFR clearance needs to be reissued when you pass through airspace that is not controlled. I am very interested in seeing a source supporting this or clear explanation why this is.
