A trust accused of funnelling "dark money" into the Scottish Conservatives has been fined after failing to report a donation of £157,000 three months before the 2017 general election.

The Scottish Unionist Association Trust (SUAT) failed to notify the Electoral Commission of a £157,350 gift it received in March 2017, along with a £50,000 donation in February 2014.

It has been under investigation by the UK's electoral watchdog for more than a year over whether it was correctly registered as a donor.

SUAT became embroiled in controversy in the summer of 2018 over allegations of secrecy, which led to the trust disclosing details of its trustees and address.

The Electoral Commission has concluded the trust is a "permissible donor" to political parties, and that the Scottish Conservatives "properly reported" gifts it received from SUAT.

However, the watchdog also found the trust failed to notify it of political contributions to the Tories exceeding £25,000 in four separate years - 2010, 2015, 2016, and 2017.

SUAT has accepted the commission's findings and has paid fines totalling around £1800 - a punishment opposition parties have dismissed as "frustrating" and "petty cash".

The electoral watchdog said the trust had "consistently failed to provide proper notification of its activities", denying the public "the transparency it was entitled to".

Under electoral law, unincorporated associations like SUAT are required to report donations which add up to more than £25,000 in any calendar year.

Each of the years where SUAT broke this rule were election years, with three general elections taking place in 2010, 2015 and 2017 along with a Holyrood election in 2016.

The trust has gifted nearly £320,000 to the Scottish Tories since 2001, and an investigation by STV News found a fifth of all declared donations to the party in the run-up to 2017's snap general election came from SUAT.

Then-leader Ruth Davidson - whose party gained 12 seats in that snap poll to increase their MPs from one to 13 - said the trust was "not in any way mysterious".

As a members association, SUAT was also required to report donations it received of more than £7500 to the commission within 30 days.

But the two gifts it received in 2014 and 2017 - totalling more than £200,000 - were not reported to the watchdog until its investigation into the trust was already under way.

Louise Edwards, director of regulation at the Electoral Commission, said: "The reporting requirements for members associations and unincorporated associations are clear, so it is always disappointing when regulated organisations fail to provide accurate reports on time.

"Properly, SUAT's donations to the Conservative and Unionist party were reported by that party and published so the public could see them.

"But SUAT consistently failed to provide proper notification of its activities as an unincorporated association and as a members association.

"As a result, the public did not have the transparency it was entitled to have of SUAT's finances.

"The commission will continue to enforce these requirements to ensure that voters have the information they need."

A spokesman for the Scottish Conservatives said: "This is a matter for the Scottish Unionist Association Trust.

"As the Electoral Commission states, these donations were properly reported by the Conservative party."

SNP MP Pete Wishart said: "The dark money scandal has been lingering around the Scottish Tories like a bad smell and we now know that serious offences have been committed by this shadowy organisation - including a damning indictment by the electoral watchdog that it had consistently failed to provide proper notification of its activities, and as a result, the public did not have the transparency it was entitled to.

"The links between SUAT and the Scottish Tories is at the heart of all of this and we need to know that this will not happen again, and that all further donations will be legal and transparent.

"Many current Tory MPs secured significant donations from SUAT which no doubt assisted them in their election campaigns."

He continued: "Political parties cannot continue to treat electoral law as an afterthought and continue to be cavalier with their financial arrangements.

"Electoral legislation is in place to protect the electorate and ensure a level and transparent playing field...

"Where SUAT will no doubt treat these derisory fines as petty cash I am grateful to the Electoral Commission for its investigation and outcome.

"We need to clean up Scottish politics and liberate it from 'dark money'."

Scottish Green MSP Ross Greer said: "The Scottish Tories have been funded by dark money for years.

"Now this damning Electoral Commission report has been published, they need to urgently explain themselves.

"For the findings to come on the same morning as a Tory cabinet minister had to apologise to an English court, for 'accidentally' illegally approving more arms sales to Saudi Arabia, shows the Conservatives' approach to the rule of law quite starkly.

"They clearly believe it's only for everyone else to follow."

He added: "It is frustrating that the fines for this substantial number of violations totalled just a small fraction of the money actually funnelled through SUAT.

"The Electoral Commission desperately needs the power to deliver substantial fines and other enforcement mechanisms.

"Otherwise, the flood of dark money which is poisoning our politics will only continue."