The ADR said that the unknown sources are income declared in the Income Tax (IT) returns but without giving source of income for donations below Rs 20,000.
According to the Association for Democratic Reforms (ADR), while the total income of 48 national and regional political parties between 2004-05 and 2014-15 stood at Rs 11,367 crore, the sources of as much as Rs 7,833 crore of it were untraceable.
Trilochan Sastry, Founder Member of ADR, said: "The income from known donors was Rs 1,835 crore (16 per cent) and income through other known sources, such as sale of assets, membership fees, bank interest, sale of publications and party levy, was Rs 1,698 crore (15 per cent)."
"However, the remaining income of Rs 7,833 crore, which works out to 69 per cent of the total income, does not have sources to attribute," he added.
The ADR said that the unknown sources are income declared in the Income Tax (IT) returns but without giving source of income for donations below Rs 20,000.
According to the report, the Bahujan Samaj Party (BSP) was the only party to declare zero donations above Rs 20,000 between 2004-2015, thus 100 per cent of party's donation came from unknown sources.
Among national parties, the Congress' income through unknown sources was 83 per cent (Rs 3,323 crore) of the total income while the BJP's share of income from unknown sources found out at 65 per cent (Rs 2,126 crore).
"Among the regional parties, 94 per cent (Rs 766 crore) of total income of the Samajwadi Party and 86 per cent (Rs 88 crore) of the total income of the Shiromani Akali Dal came from unknown sources," reads the report.
Jagdeep Chhokar, Founder Member of ADR, said that transparency in political donations was necessary in the fight to curb black money.
"We do not know the source of major chunk of donations the political parties received, which will make fight against the black money difficult. Until transparency is brought in the political funding, nothing is going to happen," Chhokar said.
The report further reveals that the income of national parties from unknown sources had increased by 313 per cent from Rs 274 crore in 2004-05 to Rs 1,131 crore in 2014-15.
In case of the regional parties, the hike was by 652 per cent from Rs 37 crore to Rs 281 crore in the 11 years.
"Among all national and regional parties, the BSP is the only party to consistently declare receiving no donations above Rs 20,000, so the party's 100 per cent came from unknown sources. The total income of the party increased by 2,057 per cent from Rs 5.19 crore in 2004-05 to Rs 111.96 crore in 2014-15," said Major General Anil Verma (retd.), Head of the ADR.
The ADR officer bearers demanded scrutiny of overseas donations to political parties in line with that of NGOs. They also sought CAG (Comptroller and Auditor General) audit of the accounts of the parties and demanded criminal action if any irregularity is found.
The Congress has the highest total income of Rs 3,982 crore during 2004-15, which is 42.92 per cent of the total income of the six national parties while the BJP has the second highest income of Rs 3,272 crore (35.27 per cent) during the same period.
The reports said that the total amount of donations above Rs 20,000 declared by the six national parties was Rs 1,405 crore. The BJP topped the list by declaring Rs 918 crore as received via voluntary contributions above Rs 20,000, which is more than twice declared by the Congress.