A report by the Association for Democratic Reforms (ADR) has revealed that the ruling BJP's income has increased by 81.18 per cent to Rs 1,034.27 crore between 2015-16 and 2016-17.
The income of the Congress, however, decreased by 14 per cent to Rs 225.36 crore in the same period.
According to the report, seven national parties -- the Bharatiya Janata Party, Congress, Bahujan Samaj Party (BSP), Nationalist Congress Party (NCP), Communist Party of India-Marxist (CPI-M), Communist Party of India (CPI) and Trinamool Congress -- have declared a total income of Rs 1,559.17 crore and expenditures of Rs 1,228.26 crore.
The report, based on the submissions made to the Election Commission, compared the total income of the BJP and Congress, their expenditure and sources of income.
"Between 2015-16 and 2016-17, the income of BJP increased by 81.18 per cent (Rs 463.41 crore) from Rs 570.86 crore to Rs 1034.27 crore while the income of the Congress decreased by 14 per cent (Rs 36.20 crore) from Rs 261.56 crore to Rs 225.36 crore," it said.
The BJP had declared expenditures of Rs 710.057 crore during 2016-17 while Congress incurred Rs 321.66 crore -- Rs 96.30 crore more than its total income.
The report said that both the parties have declared "donations/ contributions" as one of their three main sources of income.
"The grant/ donations/ contributions of Rs 997.12 crore declared by the BJP forms 96.41 per cent of the total income of the party during 2016-17. Declaration of Rs 115.644 crore under revenue from issuance of coupons by the Congress forms top most income of the party, contributing 51.32 per cent of its total income during the fiscal," it added.
The report said that the seven national parties collected a maximum of 74.98 per cent (Rs 1,169.07 crore) income from voluntary contributions for 2016-17.
Voluntary contributions accounted for 60 per cent (Rs 616.05 crore) of their income in the previous fiscal.
These parties received Rs 128.60 crore income in bank interest in the same fiscal.
The release said that the due date for submission of annual audited accounts for the parties was October 30, 2017, but the BJP submitted its report on Februray 8 and Congress on March 19.
The ADR said the BJP, Congress, NCP and CPI have consistently delayed submitting their audit reports for the past five years.
It demanded the political parties to provide all information on their finances under the Right to Information Act as a step to strengthen elections and democracy.
"Full details of all donors should be made available for public scrutiny under the RTI," the report said, adding that countries such as Bhutan, Nepal, Germany, France, Italy, Brazil, Bulgaria, the US and Japan have done so.
It said the Election Commission should ensure that no part of the Form 24A submitted by political parties providing details of donations above Rs 20,000 should be left blank.
The ADR said that a political party which does not submit its Income Tax returns on or before the due date should be given tax exemption and should be de-recognised.