"The first duty of any government is to keep our country safe and I firmly believe that leaving the EU would fail that test… The lesson from Paris is clear: to tackle terrorism we must stand shoulder to shoulder with our allies in Europe. The security of Britain is inextricably linked to staying in Europe," Johnson, a former Home Secretary, will say at the event to launch the campaign in the UK city of Birmingham, as quoted by the BBC.
According to the official, the United Kingdom is "stronger when working with our allies, committed to peace, democracy and international law" amid the current geopolitical situation.
UK citizens are expected to vote in a referendum by the end of 2017 on a so-called Brexit, Britain’s exit from the European Union, as promised by Prime Minister David Cameron during his pre-election campaign earlier this year.
Cameron has repeatedly said that EU membership is beneficial for the United Kingdom, but only if the bloc were to implement new reforms. He pledged to achieve the reforms first, and then hold the referendum.