Loath as I am to comment on stuff I don't know about, I wouldn't be so quick to accept that planning permission is required.
The issue seems to be whether you're planning on landing at this location on a regular basis. If not, then you haven't "rendered the use regular". Look at case RL2262 (in the link by raven2), which seems to be the only relevant one (as I take it you're not talking about basing a helicopter there, with hangers, etc.). The following points are included in the justification for the decision:
(iv) the proposed activity would establish a consistent pattern of use that would render the use regular,
(v) the character of the use of the open space lands would be altered in planning terms by the proposed use...
MQ.