Yes, do the maths.  40% of votes cast, 45% turnout, that's just 18% of those eligible to vote.  And the Tories are hailing this as an historic victory.

How on earth can this be democratic?

If all parties combined fail to persuade 50% of the population to vote, then none of them deserve to represent the constituency. 

In such cases, surely a representative selected at random from the electoral roll would have more legitimacy.