On 30 April 2010 the Guardian declared in a long editorial: "If the Guardian had a vote in the 2010 general election it would be cast enthusiastically for the Liberal Democrats."

This was a break with recent tradition as the Guardian had long since sought its "place on the left" under the editorship of Alastair Hetherington in the 60s. But before that it was both a liberal and a Liberal newspaper – CP Scott was himself a Liberal MP even while he was the editor.

The decision to shift allegiance was by no means on a whim. Seven days before the editorial appeared there was the traditional pre-election open meeting of Guardian editorial staff, whose opinions were sought as to which party should get the paper's vote. Earlier that same day, readers had been asked to post their views in an open thread, and their responses were given in the meeting.

Matt Seaton, then editor of Comment is free, wrote on 23 April 2010: "Between 7:30am and the start of the meeting at 1:15pm, in excess of 1,200 comments were posted. While this is no scientific sample (and no opinion poll), an overwhelming majority of commenters urged the Guardian to back the Liberal Democrats. But just as significantly, the key reason why most of those who posted wish to see that is … because you want to see real political change, vitally including electoral reform."

However, many other traditional readers were shocked by the decision to turn to the Lib Dems. Ever since, the readers' editor has received a steady stream of letters complaining about that decision and the perception of continuing support, as well as scores of comments below the line echoing the same sentiments, often under the avatar of the Peterloo Massacre.

Here is an early, fairly typical, email from a reader, sent on 11 November 2010. It refers to the main reason given in the editorial for the move – the chance for proportional representation: "In view of the coalition's progress so far, do you now regret your editorial advising readers to vote Lib Dem? I could hardly believe this so-called advice from a left-leaning paper, merely it would appear for a chance to have a referendum on the voting system, and a second-class one at that. It reminds me of Thomas More in A Man for All Seasons saying to his betrayer, Richie Rich, 'But for Wales, Rich, for Wales!!!'"

Polly Toynbee addressed the issue a year later on 16 September 2011, on the eve of the Lib Dem conference, in the face of continuing criticism.

But the criticism continued. Here is another letter in November 2011: "I love and look forward to picking up the Guardian – but you do get some really important issues wrong, like supporting the Lib Dems at the last election. Say sorry to the many hard-working teachers and public-sector workers who read the paper."

Readers are still angry. As we are now past the halfway point to the next election as well as the 2013 Liberal Democratic conference, it seems an appropriate time to examine the readers' continuing concern.

Here is a letter on 20 September 2013: "I have become disillusioned over the last three years as the Guardian continues to support, almost overwhelmingly, the actions of the Lib Dems within the coalition government. The final straw was today's paper (20 September) in which we have yet more Clegg mania, with pretty coloured photos of Clegg and family splattered over the paper. We also had several pages clearly aimed at embarrassing the Labour party. After 45 years of subscribing to the Guardian, I get no pleasure in writing this letter."

And another: "I'm dismayed by the continued editorial support for the Lib Dems in the Graun. I don't agree with what the Lib Dems are doing (I am one of many betrayed by them) and I don't understand why you seem to think that they are a good thing. I would like you to be more objective and less biased in your political analysis. However, as that is unlikely, the next best thing is for you to explain, in print, why you are taking this approach and what the cost would be of being a bit more principled."

Are we still "enthusiastic"? I will be putting the readers' concerns to Alan Rusbridger, the Guardian's editor-in-chief, next week.