Unfortunately it is true
There is no system like in the States to collect your clearance on the ground or by telephone with a clearance void time).
Depending where you are flying from, you may be able to get a LARS or other radar unit to negotiate the clearance with the airways control unit. They will typically give you a squawk and RIS/RAS while they coordinate with the airways guys. They will then hand you over to the appropriate frequency for the actual clearance.
If there is no local friendly unit then it is a call to London Information to activate your flight plan and do the coordination.
On the routes that I fly, there is a long distance I can run underneath the aiway and outside controlled airspace while the clearance is coordinated.