By Dominic Casciani
BBC News community affairs reporter
Recent history tells us two things about immigration: That nations are seldom sure about what they think of it - and that the party in power ends up on the defensive if immigration rises.
Asylum applications: Down over two years
So when Labour got politically hammered in its heartlands over immigration in the 1960s, cabinet minister Richard Crossman noted in his diaries that it was the "greatest potential vote-loser if we are seen to be permitting a flood of immigrants to come in and blight the central areas in all our cities".
Today that historic fear stalks Labour again as it battles to maintain trust over who comes and goes from Britain.
Immigration has been a big issue for a good five years. It emerged amid the rise in asylum numbers and has ratcheted up a political notch every time Labour has been seen to falter, even if events are not of the government's making.
IS IT DEVOLVED?
Scotland: Not Devolved
NI: Not Devolved
Devolved issues are the responsibility of the Scottish Parliament,
Welsh Assembly, or NI Assembly
Mori's monthly political attitudes poll has consistently recorded immigration as one of the top concerns among those questioned. And a recent YouGov poll found a majority saying new arrivals put pressure on public services.
So how important is immigration to this election? It is certainly a headache for Labour, which would prefer its battlegrounds to be the economy and public services.
But what makes immigration such an additional headache for a government trying to defend its record is how it plays on the doorstep.
If levels of anger or frustration over immigration are really as high as they appear, this could have an effect on Labour's ability to get out voters in some areas.
In most of these cases, people have expressed familiar fears over what immigration means when it comes to housing, school places or crime. Many of these fears are also being articulated by some in Britain's ethnic minorities.
Asylum figures began rising in the UK before Labour came to power in 1997. They reached a record high in 2002 and have been falling back since then.
At the same time, we have witnessed a steady rise in the majority forms of immigration - family reunion, workers and students.
This rise has coincided both with Tony Blair's tenure of Number 10 and the continued buoyancy of the economy.
The first charge from Labour's critics is that the government badly handled asylum, causing institutional chaos and breakdown.
The party inherited a backlog in undecided from the Conservatives and that backlog then grew. After three major Acts to reform the system and falls in numbers, the cases have dropped back down to something more manageable.
Labour took a significant hit when it had to ditch its target to remove 30,000 failed applicants in a single year after it proved completely undoable.
Since then it has invested heavily in removing failed asylum seekers and the numbers have risen - although only 1 in 15 of last year's failed applicants have been removed.
The one thing nobody really talks about is the quality of the decisions. These have worsened over the years - meaning more costly appeals and support while applicants wait for an outcome. At present a fifth of those who appeal win.
Finally there is the issue of international comparisons. The UK became the top host among industrialised nations - but has now dropped to third behind France and the USA.
The second more complicated charge against Labour is that it either relaxed controls on general immigration without telling anyone, or simply lost control.
Until his resignation, former Home Secretary David Blunkett devoted a great deal of time to refuting this charge.
Community anxieties: Can the politicians reassure?
At its most combative, Labour stands by Mr Blunkett's 2003 position that there is "no obvious limit" to sensibly-handled economic immigration and that it has done the right thing to allow in more people to work.
It has sought to increase public confidence in economic migration by proposing a points-based entry system used in other countries (and virtually indistinguishable from the Conservative proposal), emphasising that it is restricting the right of non-EU foreigners to settle permanently.
But this is where things get tricky because there has been little debate about the effects, even though this seems to be what concerns the public.
And it's here where the Conservatives have been attacking, with accusations that communities are being strained by arrivals, that schools are struggling with multiple languages and that something has to be done to monitor migrants' health.
The Conservatives have backed up this tough talk with proposals for quotas for refugees and economic migrants. Asylum seekers would not be allowed to come to the UK at all, they would be processed offshore by an as yet unnamed partner country - somewhere Labour has dubbed "Fantasy Island".
The Conservatives also want get tough with employers who employ immigrants by requiring them to post a bond, worth six months' salary, for each immigrant they employ.
And they have argued that a new border police force should be set up to guard the UK's ports of entry.
The Liberal Democrats argue that immigration cannot be reduced to simple sound bites because it is so open to misinterpretation, historic anxieties and xenophobia.
They want to create a system that focuses on getting asylum decisions right first time - and provide a flexible work migration system within a European framework. The most controversial Lib Dem proposal is to lift the bar on asylum seekers working.
Although immigration is decided at a UK level, the debate on is shaping up slightly differently in Scotland, where there are concerns about declining population.
The ruling Scottish Executive is reported to be considering taking migrants who are not wanted elsewhere in the UK, and the SNP wants a campaign to encourage Scottish ex-pats to return.
Whoever wins on polling day, immigration will not disappear from the political agenda or from public debate.
Given some recent events, including documented racist violence in cities or public meetings where residents are clearly frightened by what new arrivals mean, the situation could quite easily worsen.
This general election will show us whether politicians are able to answer these voters' concerns and explain how and why Britain has been changing around them.