I highly recommend a post by Stuart Wilks-Heeg and Stephen Crone of Democratic Audit, writing at the LSE blog, on trends in British opinion regarding proportionality.
A short summary would be that public support for the principles of proportionality or “fairness” vs. “effective government” has been quite stable over the past three decades. However, results of polls that specifically reference a possible shift to a PR system have been more volatile. There was a sharp, but temporary, uptick in support for a PR system according to polling in 2009, yet in 2010 there was a sharp increase in opposition to PR.
In other words, while underlying democratic values may not have changed, the public has become more polarized about the issue of adopting of a proportional representation system.