An animated history of the European UnionIBTimes UK

Former defence secretary and Conservative MP Liam Fox has claimed the UK cannot reduce net migration if it remains in the European Union. Fox, a Vote Leave supporter, said the Conservative manifesto pledge to reduce immigration to below 100,000 could have been achieved only if the UK had not been part of the EU.

"No Conservative MP who was elected in the last election can fulfil our pledge to the British people on immigration if we stay in the European Union," he told the BBC. "It was entirely possible, but only if we left the EU. This is not a distraction, it is a huge issue for many people who are facing the implications of this immigration in their real lives."

Fox's comments came as a research by the Office for National Statistics (ONS) showed that net migration climbed to 333,000 in 2015, increasing by more than 22,000 compared to the same period in 2014.

Prime Minister David Cameron has come under fire on 29 May after failing to cut net migration down to "tens of thousands", as promised. Former London mayor Boris Johnson and Conservative politician Michael Gove attacked the PM in an open letter, claiming the pledge on net migration was "plainly not achievable" while the UK stayed in the EU.

A Downing Street source said these accusations were an attempt to distract people from the negative consequences of leaving the EU. "This is a transparent attempt to distract from the fact that the overwhelming majority of economists and businesses believe leaving the single market would be disastrous for jobs, prices and opportunities for people," the source said.

A referendum on whether the UK will continue to stay in the EU or not will be held on 23 June. Pro-EU Cameron warned a Brexit could lead to economic uncertainty and financial pain, something pro-Leave supporters dispute.

EU referendum: This is what you really need to know about the Brexit voteIBTimes UK