Hmm... A few thoughts from someone with no legal training...
If you go into a cafe and they charge you £1000 for a cup of coffee, you don't have to pay unless the price was agreed in advance. If they charge you £4 it may still be an expensive cup of coffee, but you have to pay. Likewise, if you impound an aircraft because the owner failed to pay a £75 landing fee, that may be OK, but if you do so because they failed to pay a £3000 landing fee I think you'd be on dodgy ground.
If you have an unmarked well on your land, and a trespasser falls down it, you can be held responsible and potentially even charged with manslaughter. Likewise, if you have something that looks like an airstrip from the air but that is not safely maintained, I can imagine there may be potential liability issues. This could particularly be the case if there are any other strips nearby that might legitimately be confused with it.
Obviously in an ideal world, everyone would phone for prior permission, but perhaps there's an old family friend somewhere who doesn't realise the previous tenants have moved and drops in unannounced. That minor error shouldn't be a death sentence.
Anyway, I would suggest to the OP, who clearly wants to do the right thing, that they simply make certain the old landing strip doesn't look like one from the air. Ploughing or planting with the right sort of crops would work. A fence along the middle wouldn't. I would worry that an old grass strip may be visible for a little while, as its texture may differ from the surrounding grass for some time.
Last edited by abgd; 4th Jun 2012 at 01:52.