The source of around 53% of the income of six national political parties in the last financial year is untraceable, the Association for Democratic Reforms said on Wednesday. The Bharatiya Janata Party alone accounted for as much as 80% of such income.

The Association for Democratic Reforms is a nonprofit that works on political accountability. Its researchers studied the tax returns and donation reports filed with the Election Commission by the BJP, the Congress, the Bahujan Samaj Party, the Nationalist Congress Party, the Trinamool Congress and the Communist Party of India. The seventh national party, the Communist Party of India (Marxist), was not covered in the study as its schedules and annexures were unavailable for 2017-’18.

The six national parties earned Rs 1,293 crore in 2017-’18, of which Rs 689 crore was declared as income from unknown sources, the report said. The BJP earned Rs 553 crore from unknown sources, the Congress Rs 120 crore, and the rest Rs 16 crore. The share of the parties’ unknown income from electoral bonds was Rs 215 crore.

Between 2004-’05 and 2017-’18, the parties collected Rs 8,721 crore from unknown sources, the report added.

The report defined “income from known sources” as donations above Rs 20,000 whose donor details were made available by the parties. Donations less than Rs 20,000 declared in tax returns as income but without identifiable sources were classified as earnings from unknown sources. Such sources include electoral bonds, coupons, relief funds, and contributions from meetings.

The Congress and the NCP earned Rs 3,574 crore through the sale of coupons between 2004-’05 and 2017-’18.

Electoral bonds are monetary instruments that citizens or corporate groups can buy from a bank and give to a political party, which is then free to redeem them for money. Union Finance Minister Arun Jaitley had announced this scheme in his Budget speech in 2017, claiming the government wanted to clean up political funding and make it a transparent process. The bank started selling the bonds from March.

However, the entire process is anonymous since no one is required to declare their purchase of these bonds and political parties do not need to declare the source of the money. The money is unlikely to be “black” since it has to be given by cheque, the government has reasoned.