London mayor warns that Britain must learn from Japan, where shrinking population has contributed to long period of economic stagnation

Boris Johnson has warned that Britain must consider the negative impact of very low immigration, as the government comes under pressure to reduce the number of migrants coming to the UK.

The London mayor made the remarks on a trade trip to Japan days after one of his possible Tory leadership rivals, Theresa May, gave a speech saying high immigration delivered almost no economic benefits.

Speaking of the Japanese economy, he 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.”

May’s speech at the Conservative party conference contained some of the strongest rhetoric against immigration of any senior politician in recent years. In contrast, Johnson has often highlighted the benefits of immigration at a time when other Conservative politicians are nervous to do so.

He used his Daily Telegraph column this week to criticise those who blame immigrants for “everything that is wrong with society”.

George Osborne, the chancellor and another possible Tory leadership candidate, is known to be relatively liberal about immigration but he is also playing a leading role in Britain’s renegotiations with the EU in an attempt to curb migration.

Speaking to CNBC at an International Monetary Fund meeting in Peru, the chancellor confirmed the UK was still seeking changes to EU migrant benefits, despite reports that this demand had been downgraded.

He said: “We are looking for substantive changes to our relationship with the European Union, to reflect the fact that we are not in the euro, that reflect our concerns about migration and people coming into our country just to claim our welfare payments … and reflect our concerns about Britain to be tied into an ever closed union.”