I saw a guy at the gym the other day wearing a Froch-Groves II t-shirt. Just so you know .

I feel that fight was the tipping point with British boxing. From then on things changed and being well known within boxing circles/fans translated to being fairly well known in a general sense too.
Before that you had to 'transcend' the sport in Britain to be known to the average man/woman on the street and only a handful did that.
After that, you could be well known to the general sporting public without having to 'transcend' the sport.
The sport itself became big enough that having a high-profile within British boxing circles became enough to have some general recognition in the wider public too.