Boris Johnson: arithmetically challenged!
The numbers that are perfectly clear are that 333,000 net immigrants entered the UK in 2015.
Boris then focussed on the 184,000 from the EU while never really addressing the 188,000 from the Non-EU and completely ignoring the 39,000 Brits emigrating.
The sum really is 184,000 EU immigrants + 188,000 non-EU immigrants – 39,000 UK emigrating from the UK = 333,000 net immigrants.
Boris has effectively been arguing 333,000 = 184,000 with the slogan he repeated over and over and over again: “333,000 immigrants entered, 184,000 from the EU. We need to take back CONTROL” The effect was that people equated all immigrants with EU immigrants exclusively.
In fact the proper comparison is probably 145,000 EU immigrants and 188,000 non-EU immigrants.
It is probably fair to assume that most if not all of the 39,000 Brits leaving are going to the EU (Spain, France). But presumably, Border Control never asks ‘where are you going?
At the extreme then, net-net EU migration could be 184,000 – 39,000 = 145,000 versus 188 with non-EU.