Yes, Britain has changed over. I don't know if there are any of the older hi-lo type sirens left in service anywhere in the country, but it must be several years since I last heard one.

The modern emergency sirens are more likely to sound something like this: http://www.met.police.uk/audio/siren2.wav

Up until the 1960s emergency vehicles here commonly used a bell -- You can see one fitted just above the front bumper in one of the pictures above.

The single rotating beacon (which was always blue in the U.K., not red) of the 1960s/1970s has also given way to multiple strobe lights in a long strip. Some of these new strobes are too bright, in my opinion.

I came upon a minor traffic accident on a dark lane one night a few weeks ago, and the patrol car was stopped at the roadside with all the lights flashing. The cop waved me through past the other cars, but by the time I was almost level with the police car I could barely see where I was going for all the strobe lights in my eyes. [Linked Image]