A BBC article states that Britain would be able "to cope" with a major solar storm on the order of the Carrington Event. An expert report on Space Weather produced by the Royal Academy of Engineering states that, for example, its power grid is designed as a lattice, so could adjust. GPS might be out for three days. One in ten satellites might be knocked offline, temporarily or permanently. The 4G cell phone service is a concern, as it is not as robust as the 3G or land line systems. It specifically contrasts that with the long lines of the Canadian power system, so there's no comfort there.
All in all, a much more optimistic result than I would have expected, but other countries might be more affected than Britain.