Shinzo Abe’s commitment to reviving the Japanese economy through deregulation came under attack from a close ally yesterday as concerns emerged at the Bank of Japan over the fight against deflation, a core element of his “Abenomics” agenda.

Hiroshi Mikitani, the internet billionaire, who advises Mr Abe as a member of the premier’s Industrial Competitiveness Council, threatened to quit in a stinging assessment of the government’s handling of drug sales liberalisation.

Mr Mikitani’s broadside, delivered at a fiery news conference, exposed deep divisions within Mr Abe’s administration over proposals for competitiveness-promoting structural reform. The premier has described such reform as the most crucial element of his campaign to end two decades of economic drift. Yet critics say his ambitions on several other fronts – including labour rules and farmland ownership – have also been delayed or watered down.