If you are on a IFR flight plan and leave controlled airspace in the UK, it is possible for you to be passed to London Info. When this happens, your IFR may be canceled, flight plan trashed, further clearance is null and void, and you are forgotten about.
This is a misunderstanding of the UK system...a flight plan is not "trashed" at all. It is not the operating methods of London Info that are out of line with the rest of the world it is the airspace structure that is...
In the UK the basic deal is that London Control are only interested in the portions of the flight that fall within the airways system, if you leave the system then they are not interested and it is up to the pilot's discretion who he talks to.
However if on leaving the airways system (being "outclimbed" by an airway or whatever) if there is still a remaining portion of the flight in the airways later on the flight plan is NOT lost or cancelled.
What has to be done is to contact London Info to negotiate an airways joining clearance for the next portion of the flight that falls within controlled airspace. They will then talk to the airways unit, the airways unit will look at the flight plan and see which bit falls within the airways system and issue a rejoining clearance on the basis of that.