carbar - You are only exempted from rule 5 when taking off or landing at a government or licensed aerodrome. If an airfield is closed, then it does not - that that time - have a licence. Therefore rule 5 applies. What does apply also is that you can't do a planned landing or take-off without the landowners permission - otherwise you are committing trespass. So, do talk to them as FD says.
DFC - Thanks for that, not quite sure how in 15 years of flying that had passed me by up to now. I shall have a play and get a feel for it.
G