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 :(
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
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 
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.
Good luck Peter but I would have filed the IFR one over London and let them sort it out.
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.
