London (AFP) - A quarter of Britons say immigrants should return to the countries they came from, according to a poll published Thursday, as figures showed the UK granted nearly a quarter of new citizenships in the European Union.

The findings come on the eve of a crucial by-election in which the UK Independence Party (UKIP) is poised to win its second parliamentary seat -- taking advantage of deep unease about immigration among the British public.

The October poll of 2,001 adults, conducted on behalf of the British Future think tank, showed 25 percent agreed with the statement "the government should insist that all immigrants should return to the countries they came from, whether they're here legally or illegally".

It follows data from Eurostat, the European Union's statistical office, showing Britain granted 193,884 immigrants citizenship in 2012, almost a quarter of the total handed out by the EU's 28 member states -- the most in the EU.

Research conducted by British Future, which focuses on identity and migration, showed that the public does not trust the country's political leaders on immigration, but that UKIP leader Nigel Farage was the least mistrusted.

The party's meteoric rise -- it won more votes than any other British party in European elections earlier this year -- has prompted Labour and the Conservatives to toughen their rhetoric on immigration.

UKIP, favourites to win Thursday's by-election in Rochester and Strood, has promised to pull Britain out of the EU, which would end the influx of migrants from other parts of Europe, and is calling for a points-based immigration system instead.

British Future highlighted the difficulties in talking about immigration, referring to a tendency by some liberals to dismiss sceptics as misinformed or racist. This risked hardening attitudes, the think tank said.

The report also contained separate surveys that showed that the public does recognise the economic benefits of immigration, and that around half of British people are in the "anxious middle" category on the issue -- neither liberals nor rejectionists.

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Its report, "How to talk about immigration", demonstrated a desire for more debate but that attitudes are more moderate than rising anti-immigration rhetoric would suggest.

"The public has far more nuanced views on immigration than is reflected in the current polarised political debate," British Future said.

"It suggests that the majority of people would be open to a sensible debate on immigration that excludes racism and prejudice."