Boris Johnson has warned Britain that low immigration can lead to Japanese style economic stagnation as he continues his trade mission to the nation.
Despite being the world's third largest economy the country has suffered from a lack of growth and the population size is falling, the mayor said ahead of a meeting with his counterpart in Tokyo.
Britons must think about the consequences of the curbing the number of people from overseas that move to the UK, he insisted.
It comes just a week after Home Secretary Theresa May gave a stark speech to the Conservative Party conference warning that mass immigration made it impossible to build a cohesive society - comments Mr Johnson was quick to distance himself from.
Speaking in Tokyo, the mayor said: "They have been going through a long period of stagnation but they are hoping to pull out of it.
"They have got demographic problems. One of the questions that people in Britain might think about is obviously that they have very, very low immigration and very, very low, in fact negative, population growth, they have got a shrinking population.
"That has, of course, contributed to the long period of economic stagnation they are going through but that has got to be seen in context. This is still an amazing, dynamic, vibrant, fantastically rich economy, the third biggest in the world and we have got to be here."
Mr Johnson will meet his Japanese counterpart to sign a deal of cooperation between the two cities on urban development, culture, transport, tourism and sporting events.
He said: "Japan is the third largest economy in the world. They wanted us to come out ages ago and we couldn't do it.
"They are now five years away from their own Olympic games, about to dispense with about £10 billion worth of contracts for their Olympics and clearly we want Britain to be front of the queue.
"We have got lots of ideas, lots of ways we think we can help."