In a reassuring vindication of British values the Court of Appeal has confirmed that ignoring a clearly worded, clearly visible sign is sufficient to count as "force" for the purposes of stopping someone claiming an easement by prescription. Further steps (including stoutly worded letters, disapproving glances, or barriers) should no longer be required.  

In the case, a Conservative club car park in Keighley was accessible to, and used by the patrons of a neighbouring fish and chip shop. The chip shop did not have a parking easement. From 1992 to 2007 the club posted a clearly visible sign stating that the car park was for members only. 

You can obtain an easement 'by prescription' if for a continuous 20 year period you use land without force, secrecy, or permission

The Court of Appeal confirmed that this sign sufficiently showed that customer parking was contentious/with force and did not entitle the chip shop owners to an easement. Landowners can take some comfort that no further steps were necessary in this case, and should take legal advice on how best to (politely) defend their property from encroachment.