I had no idea about this. It's been operating since 2002, and it sounds quite complex, but could still be really helpful.
There's a link to a "how to" guide in the middle of the article, and this is what it leads to: https://www.policeconduct.gov.uk/sites/ ... _guide.pdf
It's basically using the "55" buttons during the call, but you have to do it in a specific way. I haven't read it properly yet
but I can't do that at this time of night 
