Whilst searching for the Statutory Instrument that extends the French control zone to the "Western Docks", I came across a pair of SIs that referenced Dover. The Air Navigation (Restriction of Flying) (Dover) (Emergency) Regulations 2016 came into effect (immediately) at 10:05 hrs 20th November 2016 and were revoked (immediately) at 16:10 hrs the same day. The purpose was to ban most aircraft from flying under 2,000 feet.
https://www.legislation.gov.uk/uksi/2016?title=Dover
Obviously I'm impressed that, even in an emergency, the law is observed (or, rather, extended to cover it), but does anyone know what the emergency was - or wasn't, if you see what I mean?