Data shows that Japan intervened three times in the forex market last year to counter the historic plunge of yen. £5.6 trillion and £729.6 billion were spent on October 21 and 24 to support the currency as it hit a 32-year low against dollar last fall, while more than nine trillion was spent in just one month to halt the fall.

The invention last year was the first since 1998. It was aimed at stopping the yen from falling more than 20% against dollar amid a widening policy gap with other central banks. Japan has kept rates low to stimulate a sluggish economy, while its global counterparts aggressively raised them to slow inflation. This divergence has led investors to seek more attractive asset returns overseas, abandoning Japanese assets.

After the first intervention in September, when ministry officials stated that they had taken "decisive action", the authorities began to hide their influence. The action made by the finance ministry on October 21 took place outside Tokyo's business hours, giving traders a hint that the intervention could happen at any time. The government also warned that it is ready to influence speculators at any time.