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Traditionally, to acquire an Easement by Prescription under the common law has required that the easement be exercised 'since time immemorial'. Since 'time immemorial' was, and still is, deemed to extend back to 1189, it was very difficult to establish that the purported easement had been in use continuously since that time.

The modern approach is to allow the easement to be prescribed if it has been in continuous use for twenty years, and if there is not reason why it could not have been in existence in 1189. Of course, all the other characteristics of an easement must also be present.