The GenDec form for overseas travel is here with a set of instructions and information on filling it out here.
The preferred way to file a flight plan is online, and a website giving full instructions on how to do this is here. You may need to set up an online account, which you can do here.
A copy of the flight plan form is here.
Should the worst happen here is a form to report an incident to the CAA.
If the incident occurs on Club premises then the Chairman or any other committee member must be notified as soon as possible.