Thousands of refugees may enter Britain if leaves EU - Cameron

British Prime Minister David Cameron addresses a joint news conference with his Polish counterpart Beata Szydlo at the Prime Minister's Chancellery in Warsaw, Poland February 5, 2016. REUTERS/Kacper Pempel

LONDON (Reuters) - Thousands of refugees could flock to Britain from France if voters decide to leave the European Union, a spokesman for David Cameron said on Monday, underlining the prime minister's stance that an exit would hurt security.

In what critics said was the start of a "campaign of fear" to try to keep voters in the European Union, the spokesman said leaving the bloc could harm an agreement with France which allows British border guards to make immigration checks there.