We’re mid-way through the campaign for the European Parliament elections – though, as yet, discussion of Britain’s role in the EU has not been the, erm, dominant story. But, still, there have been five polls to date in May specifically asking for the public’s Euro voting intentions, so let’s check out what they’ve been saying:

Here they are in chronological order:

When I do the monthly LDV poll round-up, I usually give the average of the three main parties. It’s a little redundant for the Euro polls because there’s so much ‘noise’ in this data – both because MPs’ expenses has become the defining issue in the past 10 days, and also because it’s quite usual as the Euro campaign goes on for minor parties to gain at the expense of the major parties.

Still for form’s sake, here are the averages (using YouGov’s ‘certain to vote’ data):

And here’s what the actual vote shares were in the 2004 Euro polls:

What to make of it so far? Well, first and most obviously, as the Euro campaign goes on, once again we see voters’ awareness of minor parties increase. The first poll of May showed figures for the main parties not so very different to the national Westminster poll ratings for the parties (Tories and Labour relatively under-performing a little, Ukip and the BNP relatively over-performing a little). The latest YouGov poll, though, shows Ukip edging out the Lib Dems for third place, and within the margin of error to overtake Labour.

Against this, it should be remembered that the YouGov exit poll in 2004 significantly over-stated Ukip support (predicting 20% against an actual 16%) while under-stating Tory support (predicting 22% against an actual 27%) – though it was pretty much spot-on for both Labour and the Lib Dems.

This might be because of sampling bias – YouGov’s critics have long argued an internet pollster cannot be wholly representative – though they have a generally impressive track record. Another factor might be that YouGov isn’t able to factor in the ability of the major parties to mount effective ‘get out the vote’ operations – this might account for Ukip’s past relative under-performance. The Euro poll also coincides with local elections in England, which will also have a hard-to-forecast impact on turn-out, both its level and the party preferences of those who do cast their ballots.

The unknowable factor at this stage – it may become clearer in the next fortnight as we see more polls – is how far the MPs’ expenses row will actually change voters’ behaviour (as opposed to what they tell opinion pollsters). So far, the Euro opinion polls have not been significantly different to the eventual Euro results last time.

What it does show, though, is two things. First, there is everything to play for. The Lib Dems are currently not so far behind Labour, and neck-and-neck with Ukip – which means we could finish either second or fourth.

And, secondly, it shows the continuing decline in traditional voter loyalties. In 2004, barely 50% of those who voted chose to cast their vote for Labour or the Tories. It seems quite likely that in 2009 this figure will be below 50%. As tribal voters lose the habit of always voting Labour/Tory, the way is open for other parties to challenge the Westminster duopoly too. And that’s an opportunity for the Lib Dems – we are, after all, the best-placed challengers to the incumbent Labour/Tory MP in over 200 constituencies.