That long fabled phrase 'the progressive majority' is used often to justify three things (implicitly and explicitly):
1) The Lib Dems/Greens/Plaid Cymru are just offshoots of Labour and someday will join back to create an unassailable party of the left.
2) People in the UK are instinctively left wing and therefore the 'Welfare State' can never be challenged.
3) The Conservative party is in the process of a very long period of decline, leading from the 18th century into the modern period.
The 1st is a peculiarly British trait because of FPTP of only seeing two sides to any argument. In our universities liberalism is recognised as a distinct ideology but on the national political scene there is only left or right. In fact, most Western European countries manage space in their political sphere to fit two Liberal parties in (e.g. The Netherlands: VVD and D66) and successful Green parties!
The 2nd is based on the assumption that the public's voting in of Labour in 1945 and the subsequent creation of the 'Welfare State' can never be challenged and has a mandate to exist until the end of time.
The 3rd is just patently not true, the 20th century was the century of the Conservative party (in statistical terms) and the 21st has started off with a big band for the right again. This kind of leftish thinking has been around for eternity, the Jacobins found that even beheading all of the monarchist conservatives just led to finding new conservatives within their own faction.
So what role does the AV referendum play in this? Well I was an activist on that campaign from early on, we pretty much thought it was a shoe-in. The left would support us, the centre would support us and we would only be opposed by that conservative minority on the right. Of course we expected conservatives within the Labour party (John Reid, David Blunkett, etc) to team up with the Conservative party itself but fundamentally we viewed the Labour party as an anti-conservative party.
This was clearly not the case, Labour voters either voted to punish Clegg or to just keep the status-quo for status-quo's sake. Which ever of these reasons, neither are derived from anti-conservative thinking. In fact what we found was that the only 'constitutional progressives' were those on the fringes of the Labour party (think social democrats and socialists) and those liberals who could get off their high horses about STV.
So why do I think we might have two conservative parties not just the Conservative's. Well, look at the formation of the Labour party. Whereas in most of Europe the main party of the left was formed by Fabianesque intellectuals, our left wing party was formed by a conglomeration of trade unions broadly supported by intellectuals. The very name 'Labour party' is a hint, its a party purely concerned with representing a certain classes interests. Just as the Conservative party protects the middle classes and above, the Labour party formed directly as a delegation of the working class.
Subsequently, we find ourselves one hundred years later with two main parties who fight for their supporters economic interests, they don't adopt a clear ideology or 'fair' way of thinking and seek to apply it to everyone, they just punch very hard for their corner.
So A Radical Liberal's Perspective concludes that the AV Referendum was just a very clear pointer to the awful reality in the UK for Liberals AND Progressives; we have two institutionalised parties who control power, access to power and the mechanisms by which we might go about changing this. Rather than shy away from the fight after the bruising AV gave Liberals, we must realise that we were naive to think that it would be that easy.
The fight to bring British political culture into the modern era should be the primary purpose of all radicals, liberals and progressives in this country, the AV referendum should just be the beginning.