That's according to research from Professor Cees van der Eijk of the University of Nottingham which compared data collected by the British Election Study survey, conducted immediately after the May 2014 European elections.
The survey asked respondents if they had voted, and how they would vote if a general election had been held at the same time.
They then had a "plausible estimate" of how the European elections results would have changed if turnout (34 per cent) had been as high as at a general elections (68 per cent). This is what they found, as detailed in Sex Lies and the Ballot Box.
Why is this the case? As Professor van der Eijk puts it, the problem with low turnout isn't necessarily that it will change the results of elections but that it has other consequences "which are not so innocuous" - notably not voting once can be habit forming, and can eventually undermine democracy.