Boris Johnson says low immigration could lead to economic stagnation

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.