Mr Davis, the Shadow Home Secretary, told the Conservative conference that Britain was already the most densely populated big country in Europe and the level of immigration was far too high. Immigrants could fill six new cities the size of Birmingham over the next three decades, he said, and pledged to take action “before it is too late”.

His remarks were criticised as opening the party to accusations of racism and there were signs of private dismay among some Conservatives as they risked triggering the first row of the conference and overshadowing carefully planned party messages.

Mr Davis told the conference that immigrants were not evenly distributed within the country but went to areas that were already the most overcrowded. This put a burden on housing, health, education and public services in areas where that burden was already heaviest.

“A Conservative government will substantially cut immigration into Britain. Uncontrolled immigration endangers the values that we in Britain rightly treasure,” he said.

“We Conservatives understand how vital it is not to threaten what makes this country so tolerant, so decent, so respectful of other people’s rights and, yes, so welcoming of people who come here.”

Immigration would be central at the next general election. Extremist parties were already seeking to exploit fears and resentments that existed and criminals ran the trade in illegal immigration, he said. Mr Davis added: “For that reason, too, we must act to secure the future, including the future of our settled immigrant populations, before it is too late.”

The hardline tone of his remarks, and the way in which his speech was seen as enhancing his credentials, should he again run in a future party leadership contest, caused anxiety among some party officials in Bournemouth. One leading moderniser on the Tory front bench also expressed private dismay at his remarks about immigration and there was public criticism from Keith Best, chief executive of the Immigration Advisory Service, and a former Tory MP and candidate for Vauxhall, who said that it could trigger accusations of racism.

Mr Best told the BBC: “I think it is regrettable. It is opening up old wounds, which could lead to allegations of racism underpinning the whole thing. I don’t think it is going to help the Conservatives. What we need is to have a sensible, reasoned debate about how we simplify the system.”

Mark Oaten, the Liberal Democrat home affairs spokesman, said: “Michael Howard said yesterday that as the son of parents who were given asylum in Britain he owed his life to this country. It is hypocritical for him to now deny modern-day refugees the same opportunities.”

Mr Davis said that a Conservative government would bring back 24-hour checks on people entering and leaving British borders, process asylum applications overseas, the policy once dubbed “asylum island”, and enforce limits on the total number of immigrants allowed into Britain each year.

Within a month of taking office a new points-based system of immigration based on the Australian model would be introduced and an annual limit set below the current figure.

Liam Fox, the Conservative co-chairman, denied that the speech gave scope for opponents to accuse the party of racism, saying: “If they decide to do that, they will make rational debate even more difficult. They would need to think long and hard before making such a preposterous accusation. Politicians have to discuss these issues in a rational and responsible way.”

Elsewhere in his speech, Mr Davis promised to provide 20,000 prison places over five years, taking Britain’s prison population to 100,000 over five years, in order to scrap the early-release scheme.

There was some confusion over how this pledge would be funded after Tory officials released a briefing note saying that the £760 million cost should be compared with more than £1 billion that society would save from imprisoning prolific criminals.

Mr Davis, however, told The Times that the capital cost would be met from savings elsewhere in Whitehall found by David James’s report of waste in government ministries.

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