What a great set of answers ! many thanks to all concerned.
I will find out what my colleague filed and what his departure clearance was, I am speaking based on anectotal evidence. If he had an IFR departure clearance and a flight plan in the system similar to mine, it must have been in controlled airspace. But it is clear that there are a number of factors in play here.
From my own trips:
Northerner - that was exactly what I wanted to know. Thanks for typing a detailled reply, really helpful. Yes, low and relatively slow. I think on both my trips FL080/N120 outbound from memory. That makes a lot of sense about the routings and the traffic flows.
In general in the LTMA we will try and give you a service if we can, but don't underestimate how complicated you can make our sectors. We try, but we are balancing all the time now and so sometimes it will be no. Nothing personal.
I knew it wasn't easy. (or personal) Just not what the complications really were. Asking so that I can try and fit in to the system better, and to judge what the alternatives are and what might happen if one is descended early on a bad weather day etc etc.
Presumably on an accepted IFR flight plan, the answer won't be an actual no, but will involve a premature descent to VFR and or a longer routing as I have experienced, Are there any suggestions that work better with the flow for (say) Ostend or Lille to Denham than what I filed ?
I had:
EBOS N0116F090 KONAN2M KONAN DCT ITVIP DCT DET N601 BPK VFR EGLD
An alternative route that validated but was a bit longer ended DET-L9-CPT - VFR EGLD Would that be easier on all concerned ? Is that more likely to be flown as filed ? or does that get in the way of heathrow departures and likely to be descended early and VFR/OCAS before say WOD? or any others that might be better? I did read the SRD and there are very few suggestions for EGLD.
Chevron - thanks, what actually happened was Thames said to descend OCAS and "Heathrow radar are happy to give you service, contact them on ... " and so I did and worked them at 2300ft from west of stapleford until time to change to denham. Outbound, no need to talk to farnborough, the clearance from london control was relayed from denham tower on start and worked just fine. My flight plan was in the system for sure in both directions. I do wonder what happened to my colleagues though. I think that he tried to bring it forward an hour and it must have got cancelled instead, so it is conceivable that he got an ( adhoc) IFR clearance out of the EBOS airspace but no flight plan and thus when the controlled airspace changed level as Jimmy and you point out he was (understandably) on his own to renegotiate or go VFR !