I will write up this little trip later, but my Great Plan worked.
I flew in solid IMC nearly all the way to CPT, starting at 2300 and then climbing to 3300 (VMC on top by then) and later 4300, and by CPT Farnborough managed to get the clearance from London Control.
It sounded like it took them about 20 minutes to get it. That is less than the record of 30 mins which London Info once took.
30kt+ of headwind all the way to EIWT, FL160 most of the way to stay in CAS.
Good luck Peter but I would have filed the IFR one over London and let them sort it out.
Peter: I have just been flying again in the UK a few days and found London Control very helpful. Flying back home from Charlton Park I started to climb out to FL180 and initially contacted London Info and told them I was IFR from Charlton Park to Rotterdam and requested to join the airways. Then I was passed over to London Radar (after getting a squawk) and all was fine.
On the route from Rotterdam to Oxford I have also been flying over London City at FL180. I could clearly see London City airport right below my wings.
Then when flying close to Luton they offered me to get some help in further decent from Luton Radar/Control who was very helpful as well while descending further and even when entering uncontrolled airspace I requested the traffic service and could remain on their frequency.
I think it also boils down to how proficient you talk on the radio and how you negotiate. If you fly regularly that then should not be a problem.
As for the route, the moment I climb out (when maybe not having filed an optimal route) I mention that I am standing by for a shortcut. I always get that arranged.
I have filed the shorter Z route.
If I can't get a handover to London Control until in Irish airspace, it will have been a bad decision 
Once that airspace border hack is in place, the route can be made even shorter:
BPK L10 BUZAD DCT MAPLE DCT TELBA DCT KARNO DCT BAGIT/N0135F070 DCT GINIS DCT LIFFY DCT WST
That route seems to work thanks to favourable rounding errors. BAGSO is exactly on the border between EIDCT and EGDCT. Now depending on rounding and therefore whether your polygon routines think BAGSO lies within EIDCT or not, EIEG400A applies (the cross border DCT ban).
It looks like I need another hack to determine whether a point lies very close to an airspace border :(
This also seems to work and is shorter than the other one that I posted earlier:
BPK DCT HEIDI N57 SAPCO PEDIG Y53 WAL L10 PENIL L70 BABRA DCT BAGSO V14 DUB DCT WST (at FL095+).
Peter,
The VFR to CPT STU KLY route seems to be 292 miles vs the route up to the north at 341 (its only 20 minutes more and you don't need to faff about getting cleared in at CPT.
On going out of CAS and then back in (within the UK), my experience (which specifically includes Weston and also Scottish airports), is that I am switched to FIR if it is going to be more than a few minutes and on my first call it is xxx Information, Nxxx with you IFR at F100 for rejoin at XXXXX in 10. They then pass some info and then get on with getting the rejoin. The only issue I have ever had was coming back from Ireland rejoining L9, where the airway control conveyed the view I hadn't had a bath when I asked to join L9 FL100 over Wales going back to Fairoaks (but I did get the clearance)
In my IFR flying I find the most difficult thing is to get them to understand you want to leave controlled airspace! They tend to keep us in as long as possible and add tens of miles to our route, when we would be happy to leave controlled airspace by descent direct to our destination.
But that just means I don't want to plan on leaving CAS. So I would fly at
Sounds very reasonable to me. UK low level CAS is messed up - rigid and not fuel efficient.
