* EU immigration rules on Bulgarians, Romanians set to ease
* Britain mulls ways to prevent new immigrant surge
* Interior minister toughens citizenship test
By Mohammed Abbas
LONDON, Jan 28 (Reuters) - Britain said on Monday it was looking at ways of curbing immigration before the European Union eases work and travel rules for Romanian and Bulgarian citizens.
The lifting of the restrictions has triggered warnings of "hordes" of immigrants and a "flood" of new arrivals in Britain's right-leaning media, riding a wave of euroscepticism as the economy falters and public resources are squeezed.
That piles pressure on Britain's ruling Conservative Party ahead of polls in 2015, in which the increasingly popular UK Independence Party - which has pledged to end "mass, uncontrolled immigration" - could split the rightist vote.
EU membership allows citizens of the 27-member bloc to work and travel anywhere within its borders. Rules governing Bulgarians and Romanians are set to ease by the end of this year, allowing unrestricted access to the EU in 2014.
"The issue here is around dealing with potential damage to the UK's labour market and potential scope for curbing immigration to that end," Prime Minister David Cameron's spokesman told reporters.
"We're in the process of considering what we may be able to do. Clearly there is a European legal framework within which we have to operate. Clearly there may be some areas where we may want to cooperate with other member states," he said.
Immigration is a sensitive issue in Britain, where many eastern Europeans, including Poles, Hungarians and Czechs, have come to work following their countries' accession to the EU.
An opinion poll this month showed that Britons see immigration as the biggest issue facing society. A poll last year found the number of immigrants to be the "worst thing" about Britain.
While Britain's economy is anaemic, it is faring better than that of many other EU members caught in the euro zone debt crisis, and its use of one of the world's most widely spoken languages also makes it an attractive destination for migrants.
Critics say Britain grossly underestimates the number of Poles and other eastern European immigrants heading to its shores, and both the Conservative and main opposition Labour party have pledged to do more to reduce immigration.
Business and universities complain that tougher immigration rules drive away talented foreigners and deter foreign students, who pay large sums to study at British universities.
MAKING BRITAIN GREAT
Migration Watch, a group that campaigns for more controlled immigration, this month issued a study estimating that immigration from Bulgaria and Romania could amount to 50,000 a year in the first five years.
It says over 3 million immigrants have arrived in Britain from all over the world since 1997, swelling its population and straining its resources.
Cameron's spokesman said the National Institute of Economic and Social Research had been commissioned to look into the impact of Bulgarian and Romanian immigration to Britain.
"I understand people's concerns. I would underline how that example (Polish immigration) shows how difficult it can be to provide reliable and robust numerical estimates. It's not straightforward at all," Cameron's spokesman said.
The spokesman did not deny media reports that plans were being considered for an advertising campaign to deter Romanians and Bulgarians from coming to Britain. The campaign would highlight state benefit restrictions and Britain's bad weather.
Reports also said Britain was considering "emergency" rules to block EU immigrants, though it is unclear how Britain could do this as an EU member. Similar plans were reported in 2012 amid fears of the euro zone's economic collapse.
"We're looking at a range of options," Cameron's spokesman said.
Separately, Britain's interior ministry launched a new test handbook for a tougher "Life in the UK" citizenship test to be introduced in March to try to reduce immigration.
The test will focus on events and people who have "contributed to making Britain great", and will cover writers such as William Shakespeare and Robert Burns, scientists such as Isaac Newton and Alexander Fleming, and politicians including Winston Churchill and Clement Attlee.