At a traffic stop the police have the option to require you to present documents at a police station within seven days if they think something is fishy.
And people do seem to exist quite happily without formal identification. As someone who has always had a passport and driving license it was a bit of an eye-opener to me, but if you don't drive and don't travel, some folks just get by without.
So if there is a requirement to have a Britcard, and to present your 'Britcard' when stopped for any reason, then it is definitely a change.
As an ex-Brit I am also used to carrying an ID and a drivers license, and I’ve always found it quite weird that you can’t get an ID card of any kind that isn’t a full-fledged passport or a drivers license.
I also don't live in the UK any more, still a brit and not yet Australian, but I have had to adjust to it being necessary to carry your license here when driving. It means I can't really leave home without my wallet, which is odd. We're getting electronic licenses before long though, hopefully.
Others like nsw are carry always
Source: I live there
Have also driven there for 15+ years and never been asked for my license.