The numbers quoted indicate much more of a sea change has occurred than I would have expected.

in the 1960s around an eighth of British voters switched their choice between elections. By the 1980s it was a fifth. At the last election Professor Edward Fieldhouse, a political scientist at the University of Manchester, and his colleagues concluded that most of the electorate were swing voters. Politicians see it on the doorstep. “In 1997 around 40% of voters were up for grabs but today it is probably around 70%,” says Jonathan Reynolds, Labour’s shadow business secretary and an MP in the north-west.

Maybe there's hope for PR within the next 20 years.