Hugh's analysis ignores a very important point.  The fringe aside, Britain is essentially a two-party system like the United States.  In Canada, first past the post oftern results in a majority government with just over a third of popular vote because we have 3 major parties.  Riding distribution further skews the results.

Should we move to proportional representation?  Maybe.  The only drawback to democracy is that it is slow.  A proportional scheme would encourage fringe politics, meaning longer debate and even slower parliamentary process.

As to the British election, I think it was a rejection of May's hubris coupled with the late realization that Brexit may not be the best course of action after all.  The attacks in London didn't help either.  It was more a rejection of May than an endorsement of Corbyn.