It's easy to do.
There are about 40M cars on the road in the UK.
Given average mileage of 7000 miles, that's about 20 mins charging on a 100KW charger per week.
Lets say that in a week a single charger could be in operation 7 - 11pm that's 16 hours a day, 112 hours a week. Each charger could therefore service 336* cars
So if every car was to be charged using fast chargers we would need 120,000 chargers.
Lets say that 75% of the time people use home/work/lower speed chargers, that would then be 30K chargers.
There are 8,400 petrol stations in the uk, lets guess that on average each has 6 pumps, that would be 50K chargers.
* this is the cheat that makes it work, you could never achieve 100% utilization. However lets say it was 50% utilisation, the number of petrol pumps is still not far off the required. If every car took 150KW, and did 5 miles/KWH, it's really not that improbable.