If there’s one thing worse than refusing to deal with an issue voters care about, it’s promising to deal with it and then failing to do so. Making promises that you cannot keep, therefore, is one of the worst things you can do – you buy good headlines tomorrow with far worse ones further down the line.

The cap on net immigration is a good example of how this short-termist approach can backfire. Due to open borders with the EU it was a guarantee the Government could not really give, and it should have been obvious that a return to growth would likely sink it by reducing emigration as well as tempting in refugees from the decline of Greece, France and other economic disaster zones.

Given that experience, it’s understandable that some members of the Government (particularly the Home Secretary) are keen to have another crack at cutting immigration.

What is less understandable is that after failing to fulfil one poorly chosen pledge, some people are now publicly and vaguely flirting with a variety of different approaches. This is dangerous – the electorate already don’t trust the parties on immigration thanks to numerous broken promises on all sides, so raising inaccurate hopes or ambitions that cannot be met is likely to raise their ire even further.

See today’s Sun on Sunday for an example of this reckless briefing:

‘Top Tories have drawn up a plan to cap immigration from poor EU nations — in a major boost for The Sun’s “red line” campaign. The move would limit the number of people coming here from countries like Romania and Bulgaria, where wages and benefits are far lower than in the UK. A senior Government source said: “We would want a limit on the numbers we take from countries with different GDPs while continuing to trade within the EU.” Closing the doors to existing EU members would tear up the founding “freedom of movement” principle that allowed 1.5 million to flock here in 2004.’

For a start, it’s slightly unclear as to what is being proposed – while the quote from the “senior source” simply says they would limit immigration from countries with lower GDP than the UK, The Sun appears to be under the impression this means “closing the doors to existing EU members”.

The latter does not necessarily follow from the former, though. The source quoted could well be referring to the regularly floated idea of limiting immigration from poorer countries when such countries newly join the EU, ie not Romania, Bulgaria or any other existing member states.

For the Government, this policy has the advantage that a) it would supposedly be easier to negotiate such a condition during accession talks, and b) even the most ardent euro-integrationist doesn’t expect any new countries to join the EU for years to come, so it effectively defers the pledge to an unspecified point in the future.

It’s unclear how the paper got from that quote to the much more radical concept of restricting immigration from existing member states. As the story says, that would indeed mean tearing up free movement of people, requiring serious treaty change. Not only would this be the first ever unpicking of an element of EU integration, but it would mean unpicking one of the elements which Brussels holds most dear.

That is a very different proposition to the airy promise of restricting immigration in future from unknown poor countries under conditions which might never arise; it’s an offer which might well excite some in its radicalism.

But here’s the danger of loose lips and looser wording – in all likelihood, this source was speaking about the former, more vague and less valuable, policy.

If he or she was indeed talking about a truly fundamental change to the EU terms of membership, then they’re yet to run up against the uncompromising nature of the Brussels institutions and the opposition of Chancellor Merkel to treaty change of any sort. As noted here in February, it simply isn’t possible to pledge to reduce immigration while remaining a member of the EU.

So why float it? Either the idea was briefed so vaguely that it was misunderstood by the newspaper, or it is pie in the sky. Whichever it is, those voters who are excited by the reports today are likely to feel badly let down when it fails to come to pass. Taking nods today for boos tomorrow is a poor, poor bargain.