Sunak warned unfunded axing of national insurance would harm services

Economists say making the policy an election pledge could cost 40bn, which is badly needed for health, education and elsewhere

Rishi Sunak has been warned against fighting an election on an unfunded plan to abolish employee national insurance amid projections the move could blow a 40bn hole in the public finances.

As the pre-election battle on the economy between the Conservatives and Labour intensified, the prime minister was on Thursday under mounting pressure to explain how the measure could be afforded while public services were crumbling.