The Mayor of London called for a “proper conversation” about how many people live in the UK and how far voters would be prepared to go to reduce the numbers.
During a phone-in on BBC London 94.9, he questioned whether it was “foreigners” that voters were actually concerned about rather than the size of the population.
“Is it people who speak a different language? Is it people who cook a different type of food? What is it?” he said.
Mr Johnson insisted that no country had enjoyed sustained economic growth without an increase in its population.
He added: “All I’m saying to people is there is a trade-off and if you go for a reduction there will be an economic price to pay.”
The Conservative mayor said a state should be “able to control its frontiers” and “proper controls” are needed at Britain’s borders.
He added: “I think we need a proper conversation about what we think the ultimate size of Britain should be.
“We are are now at 62/63 perhaps even 64 million now. Is that too many?
“If it is too many then by how many would people like that number reduced and how would they like it to be reduced?
“And, what are they seriously calling for? Are we calling for sterilisation? Are we calling for a Chinese-style one- baby policy?”
He added: “How would people feel if the population pressure was caused entirely by white Anglo Saxon protestant babies?
“How would they feel about that?
“I just think there is a lack of clarity about that and I think people need to ask themselves what they are really…”