It's the RBS system picking up a signal from the continent (Belgium by the looks of things), I think.
Early 90s when I made visits to The Netherlands, often the BBC 1 and 2 signals (as received from Dover) would start to degrade, owing to atmospheric conditions etc. If there was complete break up, a locally generated caption would
cut in, with the words, 'BBC gebroken', I don't know whether that automatically cut in, or an operator manually
cut it up. Overnight, after BBC 1 and 2 had closed down, there would be a local test card, with BBC Radio 2 audio.
There were (still are) of cable companies in the Benelux states, however I think they all sourced BBC 1 and 2 from the same receiving station near Zeebrugge, that received the signals from the Dover transmitter. The BBC replaced the analogue transmitters at Dover in the early 00s, (which given the push for DTT
at that time was a remarkable thing to do) because its potential audience was the entire population of The Netherlands, Belgium and Luxembourg, and a source of revenue.
You might say it was a waste of money, because come 2003, the BBC went FTA on D-Sat, and the Benelux cable cos all switched to receiving via satellite, (and the quality and reliability increased dramatically of course)