By Costas Pitas
LONDON (Reuters) - Net migration to Britain reached its second highest level on record last year, according to official data on Thursday that fed immediately into the increasingly bitter debate over whether the country should stay in the European Union.
The Office for National Statistics, in its last immigration report before the June 23 vote on continued EU membership, said net migration hit 333,000 in 2015, the second-highest level for a 12-month period since records began in 1975.
Of those, 184,000 net came from the EU, which mandates freedom of movement.
The ONS said that most of the net increase - 20,000 - was due to fewer people leaving the country.
The numbers were seized upon by those campaigning for Britain to leave the EU. They argue that the country would be better able to control migration flows from outside the bloc.
"We would be able to decide our immigration policy on the needs of the British economy," Boris Johnson, figurehead of the "Out" camp, told Sky News television.
"Remain" campaigners responded by saying that immigration issues could not be solved by leaving a bloc they believe is a huge boon to Britain's economy.
In 2010, Prime Minister David Cameron promised to reduce the annual level of net migration -- those arriving minus those leaving -- to below 100,000 but has failed to keep his pledge, partly due to net migration from the EU, which accounted for half the year-on-year increase.
Immigration and the economy have consistently ranked as two of the most important issues in the EU referendum, but Immigration Minister James Brokenshire said leaving the bloc was not the solution.
"We need to continue the reforms to reduce net migration from outside of Europe, which still maintains the majority (of new arrivals)," he said.
In February, Cameron negotiated a deal with European partners to curb some welfare payments to new EU migrants which he says addresses public concerns about the level of immigration.
Critics say it will do nothing to reduce the number of people coming to Britain attracted by higher wages than in their home countries, the presence of large communities of migrants, the English language and other factors.
But with four weeks to go before Britons head to the polls, the number of migrants arriving on France's north coast in Calais has grown in recent months according to official figures released on Thursday, with many seeking to reach Britain.
The total number of people in tents, shanties and a new state-run city of converted shipping containers has reached 3,900 compared to 3,500 at the end of March, according to the Pas de Calais region.
The British government has previously warned that refugees could flock to Britain from France if voters back Brexit and France has said it could end border controls and let thousands cross the Channel in the event of an 'Out' vote.