A simple VFR route like
DCT ASTRA DCT NEDUL DCT GIBSO DCT at 2500ft
works fine and is accepted by IFPS (just tried it).
The problem is that when you depart from Lydd, they will realise you are not using the enroute IFR system and will not hand you over to London Control, so you will not get any kind of IFR service, and you may as well fly it non-radio. They will hand you over to London Info, which won't give you any CAS transit and no radar service.
If you wanted to get the pukka airway service, radar all the way, you need to file a decisive airway flight plan with a high level route, and the one I can get now is
LYD R803 MID R8 SAM R41 NORRY L9 BCN N864 EXMOR
which files at FL100 but is a totally silly route with a massive 60% overhead over GC. And you won't fly that route either because London Control will give you something else...
The only point in bothering to go "proper IFR" in a case like this is if you want to climb above icing layers, which you can't do in this region otherwise because Class A base is FL055 or lower.
A "tower" should send an IFR FP to IFPS (Eurocontrol) but sometimes they don't, when it is obvious that you are just messing about at low level, and they treat it as VFR and send it to the destination and FIS (London Info) only.