At an EU referendum event, the Leave campaigner advocated an amnesty for illegal immigrants who have been in Britain for 12 years.
Mr Johnson also called for an Australian-style immigration points system would enable Britain to "take back control" of its immigration policy.
The death of Labour MP Jo Cox should inspire a less divisive political debate, Chancellor George Osborne has said.
Speaking on ITV's Peston on Sunday, Mr Osborne said there should be less "baseless assertions and inflammatory rhetoric" in the lead up to the June 23 referendum, and more "reasoned argument and facts".
He said there was a distinction to be made between addressing legitimate concerns about migration and “whipping up division” or "putting up that disgusting and vile poster that Nigel Farage did, which had echoes of literature used in the 1930s".
The chancellor paid tribute to Ms Cox and said he hopes there will be a memorial at Westminster "not just to her tragic death but to her incredible life".
Addressing the topic of the upcoming referendum, Mr Osborne said there would be no turning back if Britain votes to leave the EU.
"It's a one-way door to a much more uncertain world, where people's jobs, and their livelihoods are at risk," he said.
"If we vote to remain, we can have a prosperous and stronger economy going forward."
In a 2013 interview, Boris Johnson says he wants Britain to be able to 'trade freely with our European friends'.
The Mail on Sunday and the Observer come out for remain while the Sunday Times and Sunday Telegraph back a Brexit.
David Cameron and George Osborne have issued an impassioned appeal for a vote for Remain, warning that Brexit would be the "big mistake"