A former Conservative MP has insisted there is "no secrecy" around donations to the party after accusations of so-called Dark Money.
The elections watchdog is currently investigating whether cash from the Scottish Unionist Association Trust (SUAT) complied with rules.
Ex-MP Peter Duncan, who resigned as an SUAT trustee 10 days ago, denied the group was trying to evade scrutiny.
He said: "I remain satisfied that the trust is a permissible donor."
Mr Duncan told the BBC's Good Morning Scotland programme: "The suggestion that this is in some way Dark Money is a bit like suggesting the WI is some KGB-front organisation.
"This is historic proceeds of tombolas and raffles throughout the west of Scotland going back 50 years.
"The were transferred into a trust with the express purpose, not of spending it, but actually investing it long-term. And that's what the trust has done since about the time I was born.
"It has invested that money with the objective of growing its capital base and making some of the proceeds available on a semi-regular basis to the party's campaigns.
"I was satisfied, and remain satisfied, that the trust is a permissible donor and that this is in no way Dark Money."
The Scottish Tories have previously said the party "always works closely with the Electoral Commission on the permissibility of donors".
An investigation by the Ferret website found that the SUAT donated £318,876 to the party between April 2001 and February 2018.
Under Electoral Commission rules, groups which make political contributions of more than £25,000 have to register with the watchdog, and report any donations in excess of £7,500.
The SUAT is not listed as an "unincorporated association" on the Electoral Commission's register, and the Commission said it was investigating whether the trust had "complied with their reporting requirements as set out in law".
SNP Westminster leader Ian Blackford challenged Theresa May at Prime Minister's Questions earlier this month to investigate donations to the Scottish Conservatives.
He claimed the Tories were "systematically shielding their donations" from view.
But Mrs May insisted that all donations to her party were "accepted and declared in accordance with the law".