Almost £4 million has been donated to campaigners on both sides of the referendum debate, with those fighting for Scotland to stay in the UK receiving over £1.2 million more than their pro-independence rivals, election watchdogs have revealed.

New figures released by the Electoral Commission show £3,965,595 was given to six registered campaigners between December 18 last year and June 26 this year.

Better Together, the lead campaign group making the case for Scotland to stay in the UK, received £2,406,475 during this period.

Pro-independence Yes Scotland was given donations totalling £1,160,000 - £1,246,475 less than Better Together.

Under the laws governing September's independence referendum, all registered campaigners must declare donations of more than £7,500.

The largest donation to the Better Together campaign so far was £1 million from Harry Potter author JK Rowling in June this year.

Drinks company William Grant and Sons has donated a total of £185,000 to those campaigning for the Union - with £135,000 going to Better Together and £25,000 to both the No Borders Campaign group and individual campaigner Angus MacDonald.

Yes Scotland received £1 million from husband and wife Colin and Chris Weir, who scooped £161 million on the EuroMillions lottery in 2011.

Bus tycoon Sir Brian Souter, chairman of the Stagecoach Group, donated £100,000 to two pro-independence groups - Christians for Independence in January and Business for Scotland in May.

Better Together campaign director Blair McDougall said: "We are humbled by the level of financial support that our campaign has been able to attract.

"The figures released today do not paint the full picture of the generosity of the thousands of Scots who have made a contribution towards keeping Scotland in the UK. When you include the thousands of smaller donations we have received, we have raised over £4 million during this period.

"What these figures tell us is that the Nationalists simply don't have a broad base of support. In addition to the wide range of bigger donations of £2.4 million reported today, we are proud to have raised an additional £1.6 million in smaller donations."

Mr McDougall also claimed the campaign for a Yes vote in the referendum is doing "whatever it can to funnel cash to front organisations".

Electoral Commission rules state that spending by an organisation working with an umbrella campaign group, such as Yes Scotland, must come off the £1.5 million spending total for that umbrella group. The rule was put in place to stop umbrella groups setting up front organisations to get around the legal spending limits.

Mr McDougall said: "Nobody can credibly believe that Yes Scotland and Business for Scotland do not meet the legal definition of 'working together'. All the signs are that the Nationalists intend to break the Electoral Commission rules on spending and working to a common plan.

"The Electoral Commission cannot wait to look into breaches of the regulations until after the final returns have been submitted. This will be after the referendum has taken place and spending limits have already been breached. This is too late in a referendum where the result is irreversible.

"The public need to have confidence in the referendum process and have to be sure that the rules are being followed. The Yes camp are operating on the basis of it is easier to get forgiveness than permission. The Electoral Commission need to take action."

Blair Jenkins, chief executive of Yes Scotland, said: 'The response from our massive grassroots support, from the Northern Isles to the Borders, has been overwhelming in its generosity. Some 10,705 have given nearly £194,173 in two months since we declared our running total in May.

"We still have a long way to go and hope that our supporters continue to help fund us to take the campaign over the finishing line with a resounding Yes vote on September 18."

Mr Jenkins criticised the No camp for "attempting to muddy the water by false and completely unsubstantiated allegations about Yes Scotland and supposed front organisations".

"Yes Scotland has followed the Electoral Commission rules from day one and continue to do so. This is a bit rich coming from a movement that is funded largely by wealthy landowners, bankers and rich Tories many of whom live outwith Scotland and don't have a vote in the referendum."

Tony Banks, owner of the Balhousie Care Group and chair of Business for Scotland, said: "More than 800 people have contributed to Business for Scotland since March 2013. Our combined cash income and support in kind over that time has amounted to £413,500. Our crowd-funding project alone raised £31,265 from more than 450 donors.

"We are grateful to every one of our contributors and stakeholder members. We're also grateful for the pledges of further funding to ensure our campaign maintains its momentum right up to polling day.

"We are equally appreciative of our hundreds of active supporters, business people who have donated time and energy to communicate the strong economic case for independence in every corner of Scotland. They are the front line making the business case for independence."