Immigration could lead to the political break-up of Britain, according to right-wing think-tank Civitas.
Immigration may threaten the UK's status as a nation, Civitas says
A pamphlet by the group suggests that Britain may have reached a "tipping point" beyond which it could no longer be seen as a single nation.
Shadow home secretary David Davis has called on the government to put a cap on those coming to the UK.
The Home Office said it had already announced a tough new points system aimed at immigrants.
The Civitas pamphlet - A Nation of Immigrants? - said the "seemingly reckless pace and scale" of immigration was bound to cause concern for people who saw the UK as a model of tolerance and freedom.
The 100-page booklet said Britain may have already reached a tipping point beyond which it could not longer be said to be a single nation.
"Once such a point is reached, political disintegration may be predicted to be not long in following," the report said.
Shadow home secretary David Davis said: "We know that unchecked immigration is putting pressure on housing and local services.
"Now this report shows that its effects are potentially even more serious."
"Given the limited number of schools, hospitals and houses, the government must apply a limit on the amount of people entering the country," he concluded.
A Home Office spokesman said the government supported legal migration which greatly benefited the economy and meant skilled migrants could fill labour gaps.
Ministers had also announced a new tough Australian-style points system for immigrants, he added.
"However, there are legitimate concerns about managing some of the effects of migration on communities. The government is listening to these concerns."
The spokesman also pointed to plans to create a panel to advise on where migrants would be best placed to fill gaps in the labour market.
David Conway, author of the Civitas report, said: "The view that Britain is a nation of immigrants suggests Britain has always experienced immigration on its present-day scale from time immemorial, which is by no means the case."