Prime Minister Gordon Brown has stepped up his pre-election rhetoric on immigration by telling would-be illegal migrants: "You are not welcome."
With Labour facing a challenge in some areas from the anti-immigration BNP, Mr Brown urged a "united front" among the main parties to combat "xenophobia".
But he said it was right for politicians to talk about immigration and address people's "needs and fears".
The Tories said Mr Brown had "failed on immigration" and had no new ideas.
In his third major speech on immigration since becoming prime minister in 2007 Mr Brown said Labour's points-based migration system for workers from outside the EU would reduce the UK economy's dependence on migrant labour as British workers were trained up to meet skills shortages.
But he also stressed the importance of addressing voters' concerns about the impact of immigration on their communities.
He highlighted recent tightening up of restrictions on newcomers and changes to housing rules to allow councils to favour local people and a new fund to help high-migration areas cope with the added pressure on public services, paid for by migrants.
'Fears'
And he delivered a stark message to illegal migrants: "To those migrants who think they can get away without making a contribution; without respecting our way of life; without honouring the values that make Britain what it is - I have only one message - you are not welcome."
Giving his reaction to Mr Brown's speech, Conservative leader David Cameron said: "I'm delighted that the prime minister has converted to the cause of controlled migration, but people will wonder what he has been doing for the last few years."
The Conservatives would broadly continue with Labour's points-based system, which sets criteria immigrants from outside the EU must meet to work in Britain, but would also set an annual cap on the number of work permits issued.
They say they want to cut net immigration - the difference between those coming into the UK and those leaving - from "about 200,000" people a year to the "tens of thousands a year we saw in the 80s and 90s".
The Conservatives say they would achieve this by stopping students transferring automatically from study to work and by capping the number of skilled workers admitted from outside the EU, although they would encourage more high value migrants such as entrepreneurs, doctors and scientists.
They would also introduce a border force to combat illegal immigration and English language test for the spouses of legal migrants.
Shadow immigration minister Chris Grayling said: "We want to continue to attract the brightest and the best people to the UK - but with control on the overall numbers coming here."
'Amnesty'
In his speech, Gordon Brown called the Tory capping plan a "pre-determined quota" which he said was "misleading" as it will not apply to 80% of migrants, including EU nationals, family members and students.
The Liberal Democrats favour a policy of earned citizenship for illegal immigrants - dubbed an "amnesty" by their opponents.
They also say they would channel skilled migrant workers to parts of the country where there are labour shortages, away from the overcrowded South-East of England.
Lib Dem home affairs spokesman Chris Huhne said there was "more consensus than meets the eye" on immigration and that "after many years of chronic mismanagement Labour have now got their act together".
But he said a border force, with police powers, was needed and he called for the reintroduction of exit and entry checks. The BNP, which is seeking to win its first seats at Westminster at the general election, want an immediate end to all immigration to the UK, including from other EU countries, and a programme of "voluntary repatriation".
The UK Independence Party is also focusing on immigration in its election campaign. It is proposing a five year freeze on immigration for permanent settlement.
UKIP wants withdrawal from the EU, like the BNP, and would end the automatic right of EU citizens to live and work in the UK, replacing it with a work permit system.
Nigel Farage, leader of UKIP's MEPs, said Britain would have an "open door" to the rest of Europe "while we are a member of the European Union".
"This is the great thing that the Labour and Conservative parties don't want the voters to know," he told the BBC News Channel.
Shortage
In his speech, Mr Brown sought to differentiate between the position of parties such as the BNP and UKIP and "mainstream parties" who he said share a consensus that immigration is a positive force in British society and a necessary contributor to economic growth.
But he told the audience "how we conduct this debate is as important as the debate itself".
And he called on mainstream parties to unite against "those who want to end immigration not because of the pressures it places on our communities but simply because they don't like migrants".
Mr Brown announced changes to the points system, which will see two occupations - care workers and chefs - on the shortage list removed.
An aide said this would only reduce numbers entering the UK from outside the EU by about 2,500 and would not come fully into effect until 2014.
Mr Brown said he wanted to encourage young British people to take up social care and catering as careers to reduce the need to employ people from outside the EU.
BBC News
