Not such a big deal for the brits to implement. Small county, relatively low population.
Also they have ISP competition, unlike the US. Remember earlier this year TWC said "there's no consumer demand" for gigabit internet? Remember when a Comcast guy said something similar? "hurr durr big country lots of people" is a poor excuse.
Assuming you are downloading 24/7 on max speeds on LTE(100mbps), you will only use 394.2TBs for a regular year(365 days)... I doubt anyone will use that much.