The law in the UK was changed a few years ago to permit this but it wasn't installed because of the cost.

A quick search turned up [1] which reckons £300 million for installation and £800,000 per annum to maintain. Which seems a bit pricey.

That said, there was a plan to trial it this year, but I can't remember if that was pre- or post-brexit.

[1]: http://www.bbc.co.uk/news/uk-england-tyne-35411297