High wing,
I think you are absolutely right. If one consults the original text in JAR-FCL, it states
(c) 20 hours of cross-country flight as pilot-in-command including a VFR cross-country flight totalling at least 540 km (300 NM) in the course of which full stop landings at two different aerodromes from the aerodrome of departure shall be made;
Unless CAA UK did this on purpose, the most probable cause is some typo just sneaked in an extra "s" in the "aerodrome of departure".
Cheers,
redbar1