Capital flight to western tax havens has shot to the top of the campaign agenda in India’s parliamentary elections as the Hindu nationalist opposition seeks to shame tax evaders, embarrass corrupt officials and win favour among voters.

The ruling Congress party tried on Monday to douse the growing furore over promises by the Bharatiya Janata party to retrieve an estimated $27bn (€20.7bn, £18bn) of so-called “black money” moved out of India and into secret bank accounts, particularly in Switzerland, each year. According to a Swiss Banking Association report in 2006, India held the largest number of bank deposits in Switzerland, above Russia, the UK and China.