KEZIA Dugdale’s leadership of Scottish Labour is under renewed pressure after three of the party's biggest donors turned off the financial tap.

One of the donors - tycoon Alan Massie - said Dugdale had to “do more” to back the Union. He issued the criticism after it emerged he and two other major financial backers had not made any registrable donations to Scottish Labour this year.

The funding black-hole covered the recent Holyrood election campaign in which the leader’s perceived softness on independence is believed to have cost her party support.

A spokesman for the Scottish Conservatives said: “It really says something when even those who bankrolled Labour are giving up on the party. It’s the latest indication that people simply don’t trust Labour either to govern or to act as an opposition.”

According to party insiders, Labour’s Scottish Parliament campaign in April was hampered by a lack of funds.

Figures from the Electoral Commission covering January to the end of June confirm the party’s lack of hefty donations.

Massie, a businessman based in Aberdeen, has donated around £295,000 to Labour since late 2011, most of which went straight to the Scottish party.

He contributed around £15,000 to Dugdale’s leadership campaign last year and gave Scottish Labour £14,450 in November, but nothing directly to the party since then.

By contrast, Massie gave £30,000 to Scottish Labour ahead of the last general election, when Jim Murphy was in charge.

Asked about Scottish Labour, Massie released a statement that praised UK leadership contender Owen Smith:

"I am committed to Labour and have donated towards Owen's leadership campaign. Indeed, I spent time with him in London last week discussing his plans for the party. Labour needs him.”

However, although Massie reiterated his support for Dugdale, he aimed a dig at her: "I also contributed to Kezia Dugdale's Scottish leadership campaign and will continue to back her but she needs to do more to emphasise the Labour Party’s commitment on Scotland's place within the UK.

"If we don't have Owen and Kezia in place, Labour faces a very long wait to form the next governments at Westminster and Holyrood."

Before the Holyrood election, Dugdale angered colleagues by saying it was "not inconceivable" she could support independence if it secured Scotland’s place in the European Union.

The remark was pounced on by the Tories, and Dugdale eventually apologised to her MSPs for the interview.

Lord Haughey, the businessman who has helped bankroll Scottish Labour in recent years, has also declined to make any direct donations to the party this year.

He has supported Labour to the tune of £423,509 since 2012, the majority of which was given to party headquarters north of the border. This included £42,000 before the last general election.

Since Dugdale became leader, Haughey has donated £30,000 to UK Labour, £2,510 to a local party in Glasgow and only £2,800 to the Scottish party directly.

Although Scottish Labour has not benefited from his largesse recently, Haughey gave £26,045 of support to former councillor Gordon Matheson’s doomed bid last year to become deputy party leader.

Haughey said he had “no comment” to make.

United Wholesale (Scotland) Ltd, which is owned by former MP Mohammed Sarwar and his family, has given around £166,000 to Scottish Labour and local parties since 2011.

Since Dugdale became leader, the only donation to show up on the Electoral Commission database to Scottish Labour was “non cash” support of £1,500 last year.

However, the firm did donate £3,000 in February to London Mayor Sadiq Khan, weeks before the Holyrood campaign began. UWS, through Labour MSP Anas Sarwar, did not comment.

Donations to the Scottish party are “registrable” if they exceed £1,500, meaning any gifts up to the value of this sum do not have to be declared.

The lack of financial contributions from these sources means Scottish Labour is dependent on trade unions and the cross-border subsidy from the UK party.

One senior party insider said: “Without the subsidies, Scottish Labour would be out of business. We simply do not have enough money coming in.”

Between January and June, Scottish Labour received a paltry amount of direct donations while constituency parties received around £30,000.

A Scottish Labour spokesman said: "We will continue to engage with business leaders across Scotland, as we set out our vision for an economy that ensures everybody can get on in life no matter their background."