GG thats not quite true to be fair - filing a plan is not mandatory for GA movements into and out of EGPD.
For those flying out of ABZ who have recently become acquainted with AFPEX it really is pretty straighforward to file a plan and there is even an abbreviated version allowing you to depart / enter the zone without all the additional info required for a regular plan.
ATC have been terriffic in accomodating local GA to these changes and have stressed on more than one occasion that filing a plan is not mandatory but desireable. They have also been at pains to stress that it is not their intention to discourage GA by encouraging the use of AFPEX but to have as far as practical GA pilots use the tools at their disposal for a safe and efficient flight to / from EGPD.
As for visiting pilots not familiar with AFPEX a telephone call / radio call will still give the desired result and response.
As a final comment - assistance with filing a plan from Signature would be restricted to the use of a PC with internet access. They cannot give training / guidance in completing the plan - that is the responsibility of the PIC.