Rising UK immigration hinders Prime Minister David Cameron's poll pledge

British Prime Minister David Cameron's pledge to cut annual net migration to below 100,000 was undermined on Thursday after figures showed the net flow of migrants coming into Britain rose by 37% to 212,000 people in the year to September 2013.

With polls regularly showing immigration to be one of the top three concerns for Britons, Cameron is under pressure ahead of European elections in May and a national election next year to make good on his promise to cut net migration to the "tens of thousands" by 2015.

Trailing in the polls, eurosceptic lawmakers in his Conservative party want him to get tough on the issue, partly because they want to stop voters defecting to the anti-European Union UK Independence Party (UKIP), which opposes "open door immigration". It risks splitting the centre-right vote in 2015.

The Office for National Statistics said on Thursday the net flow of long-term migrants into Britain had increased by more than 37% in the year to September 2013 from 154,000 in 2012 to 212,000.

The number of EU nationals who came to Britain had increased by 40%, it said, saying the number of nationals from Romania and Bulgaria had risen sharply ahead of the removal of restrictions on their right to work in Britain in 2014.

Immigration minister James Brokenshire told BBC TV the government was doing its best. "Our focus absolutely remains on bringing net migration down to those sustainable levels and we are taking action on EU migration by dealing with abuses of free movement," he said.