I am planning a flight tomorrow from outside R112 to withinR112. I am perplexed as to how I activate a flight plan from a remote airfieldoutside of R112, say a grass strip? Do I call Cranfield, for example, oranother ATC unit once airborne to activate it, or do I have to do it on theground, if do how?

Then I assume I just cancel the flight plan when I land?