Lottery winners Colin and Chris Weir have given £2.5 million to the pro-independence campaign in the past year, donation figures have revealed.
The figure is £500,000 more than previously thought and takes their total donations to £3.5m.
The Weirs are long-term SNP supporters and have previously given £1m to Yes Scotland.
In a letter published in The Scotsman last week, the couple – who won £161m from the EuroMillions lottery in 2011 – defended their right to donate to the Yes movement and described their dismay at the criticism and abuse they have been subjected to since, as a result of their political beliefs.
In it, they said: “As life-long supporters of independence, it would be strange if we did not support the Yes Scotland campaign. So that is what we have done, nothing more and nothing less.”
New figures published by Yes Scotland showed the pair have each given £1.25m to the official pro-independence campaign since 1 April, 2013.
Yes Scotland said that it has received more than £3m in donations in the past year. More than 11,000 donors have each given up to £7,500, totalling £473,000.
A further £2,678,000 has been given in larger donations from seven individual supporters.
Yes Scotland chief executive Blair Jenkins said: “We greatly appreciate and are hugely encouraged by the thousands of people across Scotland who have made donations, both large and small.”
The others who gave large donations were Randall Foggie, who gave £60,000 and Dan Macdonald and Mark Shaw who donated £50,000 each. Norman Easton donated £10,000 while Mary McCabe gave £8,000.
Better Together said the fact that the nationalist campaign relies on one source for nearly 80 per cent of funding was proof that Yes Scotland had little support beyond “the usual SNP sources”.
Better Together campaign director Blair McDougall said: “No-one would criticise the Weirs, who are long-standing SNP supporters.
“It is extraordinary that compared to the tens of thousands of small donations received by Better Together from our supporters, almost 80 per cent of Yes Scotland’s money comes from one source. We now know why they have been hiding their donations for so long.
“It is clear that the nationalists are almost completely dependent on one source of income. With a new poll showing just a third of Scots support leaving the UK, these donor details confirm that Yes Scotland is little more than a front for Alex Salmond’s SNP.”
At present, there are no limits on how much each campaign can spend in the referendum campaign.
However, on 30 May, the final 16-week phase is entered which brings with it strict limits on spending by the two campaigns, plus political parties and other participants. After this date, spending for both Yes Scotland and Better Together will be capped at £1.5m.