The flood warning siren in Lough, Lincolnshire was used for real for the first time in decades today, as can be seen in this BBC report. Lincolnshire has 46 flood sirens across its county, and I'm guessing by the flooding that's hit across this country this wasn't the only town that would've had to use them.
http://news.bbc.co.uk/player/nol/newsid ... w=bb&mp=rm
(BBC report clips are amended and updated regularly but siren was in report at 25th June 16:00 GMT)