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Ms May's remarks, which were sent out ahead of her delivery later on Tuesday, was sparking intense debate on social media.
Nigel Farage said the Home Secretary had admitted that "open door mass immigration has had a negative impact" and said the only solution was for Britain to leave the European Union.
"Tories have clearly failed on their “tens of thousands” net migration pledge," the Ukip leader wrote on Twitter.
Meanwhile, Labour's Diane Abbott accused Ms May of getting "down in the gutter with Ukip" to chase votes for her leadership bid.
In a speech at the Conservative Party conference in Manchester, she will say the “desire for a better life is perfectly understandable”. She will add: “There are millions of people in poorer countries who would love to live in Britain, and there is a limit to the amount of immigration any country can and should take.
“While we must fulfil our moral duty to help people in desperate need, we must also have an immigration system that allows us to control who comes to our country.
“Because when immigration is too high, when the pace of change is too fast, it's impossible to build a cohesive society. It's difficult for schools and hospitals and core infrastructure like housing and transport to cope. And we know that for people in low-paid jobs, wages are forced down even further while some people are forced out of work altogether.
“But even if we could manage all the consequences of mass immigration, Britain does not need net migration in the hundreds of thousands every year.”
Meanwhile, Boris Johnson will warn the Tory leadership to protect the lowest paid as it reforms welfare amid growing calls for Chancellor George Osborne to rethink cuts to tax credits.
But David Cameron has defended the cuts, insisting they are part of an overall package that “help make work pay” and claiming that some families will be £2,400 better off under the reforms.
Mr Johnson will appear alongside Zac Goldsmith, the Conservative candidate to replace him in City Hall at May's mayoral elections.
Additional reporting by PA
