Variously reported as a newspaper headline or a weather forecaster’s comment. It is almost certainly apocryphal. It persists and has currency because it is funny and brings smiles to peoples’ faces. It still brings a smile to my face, and I’ve heard it many times.
The joke persists because it speaks to the Little Englander tradition, which emerged in political debates about attitudes to Empire in the 19th century and is still used in political debate.

Geographically, Britain is an off-shore island of the European landmass, often described as a continent but attached to Asia. On a Chinese map of the world, centred on the Pacific, the British Isles are on the edge of the world. Much as New Zealand is on the edge of our Mercator maps which centre on the Mediterranean.
The “fog in the channel” quip is on my mind because I feel increasingly cut off from Europe as new post-Brexit regulations disrupt travel. As the UK imposes more customs regulations on imports from the EU late this year, we expect more congestion and delays at channel ports. Operation Brock with lorries queuing for miles down the M20 in Kent causes congestion across the county.
In what feels like a sick joke P&O’s Cyprus registered Spirit of Britain ceased sailing Dover – Calais when P&O sacked the crew on 17 March; over a month later, it has just begun sailing again. Spirit of Britain.