One of the least edifying rhetorical tools used by politicians is the anonymous voter. These faceless puppets are used to deliver whatever message the politician really wants to put across, but daren't say themselves. They are not really people, but caricatures. They are no more representative of the diversity of the British public than the cast of a BBC3 sitcom. Their only real purpose is to distance a politician from whatever unpalatable point they're trying to make.

There was a particularly unpleasant example of this during yesterday's Labour leadership hustings in Dublin. Speaking about the need to win back voters from Ukip, Andy Burnham told a story about a man who claimed he felt isolated at work, because none of his colleagues spoke English.

The man told Burnham (and we'll have to take his word for this) that he sits on his own during his lunch breaks because not a single one of his colleagues is able to speak the language.

The man allegedly told him: "When you're at work and you have a tea break, you go into the tea room and have a chat with people. When I'm at work I have my tea break on my own because I'm the only one who speaks English."

Now according to the last census, just 0.2% of the UK population are unable to speak any English – around 100,000 people. Most of these are likely to be newly arrived migrants or those who rely largely on their family and have yet to pick up the language.

These figures are broadly what you would expect in any country that isn't a prison state. As long as a certain amount of migration is allowed, then there will always be a small percentage of people who are initially unable to speak the national language. How much of a problem you believe this to be depends on your point of view, but the numbers are relatively small.

Of course it's theoretically possible that all of these people are concentrated in Andy Burnham's constituency and at this nameless voter's workplace. However, it seems rather more likely that the story isn't entirely true.

But instead of questioning the man's account or trying to put it into context, Burnham used it to claim that politicians "don't get it" on immigration. Except of course he didn't claim this. Instead he used his anonymous voter to claim it for him.

There is something particularly cowardly about this approach. When Nigel Farage spoke about feeling uncomfortable hearing foreign voices on trains, he was widely condemned. When he said he would not like a group of Romanian men to move next door, he was rightly attacked. But at least in Farage's case he had the courage to say these things himself, rather than to ventriloquise them into the words of an anonymous voter.

And at least in Farage's case we have some idea what he wants to do about it. For Ukip, the solution to hearing foreign voices in the workplace, is to leave the EU and close the borders. You may agree or disagree with this approach, but at least it's clear what it is. In Burnham's case we basically have no idea.

Now I'm not saying that Labour shouldn't be talking about immigration and Ukip. Immigration is an important subject for large numbers of voters. However, any debate about immigration should be based on facts rather than anecdotes and Labour candidates should make clear what it is they actually believe and want to do about it. If Burnham agrees with Farage that there are too many foreign voices in the UK then he should say so. If on the other hand (as seems more likely) he doesn't, then he should be honest about it. Simply repeating questionable anecdotes about workplaces where nobody speaks English does not even begin to deal with people's concerns about immigration. Instead it merely amplifies them.

Labour also need to be clear about why they lost the last election. Of course it's true that Labour did lose votes to Ukip, but of the 258 seats Labour won in 2010, not a single one was lost to Farage's party last month. By contrast Labour fell short in dozens of Conservative seats and lost 40 to the SNP. Now it's possible that Ukip will one day start to take seats from Labour as well, but when Labour already have so many real battles to fight against the Tories and the SNP to get back into government, it seems rather foolish to concentrate on hypothetical future battles against Ukip instead.

Immigration is a major concern for voters but it is not the main reason why Labour lost the election. The overwhelming reason why David Cameron is in Downing Street rather then Ed Miliband, is not because voters trust the Conservatives more on immigration, but because they trust them more on the economy. Partly this is because the economy has improved in recent years. You won't hear Cameron talking about this of course, but one big reason for that improvement is the increased number of migrants coming to work here in recent years. Without that increased migration, the vast majority of people living here who can speak English would be significantly worse off.

None of the Labour leadership candidates seem to want to talk about any of this. Winning back trust on the economy is hard and takes time. Raising fears about immigration is much easier and takes less time. However, if Labour are serious about getting back into power they should concentrate more on the former and rather less on the latter.