THE economy, housing, education, unemployment, health, the environment, foreign policy, constitutional change - there are any number of issues on which the forthcoming General Election might turn. Why, then, does immigration continually top polls of voters' concerns? One easy answer is the UK Independence Party, which has been very successful in keeping their chief selling-point at the forefront of people's minds. Anxiety about immigration long predates the formation of UKIP, however, and the main political parties have tussled since the 1960s over which can sound the toughest, a competition usually won by the Conservatives. The rhetoric appears to have little effect on net migration, which has just been recorded at 298,000 for 2014, three times higher than the Government's "no ifs, no buts" target. Politicians seem to believe that the electorate is too stupid to grasp the impossibility of holding to a target when the sum includes such imponderables as the number of students wishing to study in the UK, the free flow of EU citizens, and the thousands of individual decisions to emigrate, or maybe wait till next year when the children are a little older. Certainly the UKIP leader, Nigel Farage, believes that voters can be convinced by a pledge to hold immigration below 50,000 a year, which would depend, of course, on departing from the European Union.

The decision to work to some sort of arbitrary number moves from being impractical to tyrannical when the fate of individuals is dependent on a system in which political pressure overrules care. The cross-party parliamentary group that looked into the use of immigration detention called on Monday for an overhaul of a process that, at the end of 2014, held 3462 people in prison. Writing on the Labour List website, the group's vice-chairman, Paul Blomfield MP, wrote: "For MPs and peers from the three main parties . . . to speak with one voice on a particularly controversial issue of immigration policy is remarkable. All the more so when that voice is for radical change." The UK was the only EU country not to set a time limit for immigration detention. Nobody should be held for more than 28 days, said the group.

If politicians really believe that this issue is a vote-winner, they should be prepared, at the very least, to commit more funding to its management. One or two newspapers ran large headlines on Tuesday to warn that the cost of immigration control was approaching £750,000 a day. The answer is to spend much more than this in the short term, in order to tackle the gross inefficiency which is at the root of much of the cruelty experienced by detainees. Almost half of those held are eventually released into the community, having been needlessly imprisoned, at great expense to the taxpayer - guilty of no crime and yet under the threat of forced removal. MPs agree about a radical reform. The electorate now needs to be convinced.