A senior minister has resigned from the Freemasons because he felt that membership of the organisation would leave him open to criticism.

Michael Russell, who has responsibility for the environment, has quit the Bute lodge after being admitted four years ago.

A spokesperson for first minister Alex Salmond said he had "no idea" if other ministers were Freemasons.

Membership of the society surfaced as an issue in the first term of the parliament when calls were made for MSPs to declare their membership.

Tory MSPs David McLetchie and Jamie McGrigor, as well as former Conservative members Brian Monteith and Phil Gallie, all admitted membership at various stages of their life.

The group, which describes itself as "one of the world's oldest secular fraternal societies", has been criticised in the past for alleged secrecy, religious bias and conspiratorial aims.

However, the Freemasons deny the claims and say they are open to people of all races and many religions.

Famous former members include national bard Robert Burns, novelist Sir Walter Scott, and former Celtic manager Jock Stein.

Russell, who was elected last year as a Nationalist MSP for the South of Scotland, quit as a Freemason last May.

His register of interest states: "On election I resigned from membership of Lodge 1120, Kyles of Bute, which I had been admitted to in December 2004."

The environment minister had been recommended to the lodge by a neighbour in Argyll, and was said to have enjoyed his time as a Mason.

But Russell, whose grandfather had also been a member, resigned after concluding that being a minister and a Freemason could lead to criticism.

He told the Sunday Herald: "I felt it was best to declare membership of the Freemasons, and in those circumstances I thought it would be best to resign from it. I did not believe it was appropriate to be a minister and a member of anything that people would be suspicious of."

He also defended the organisation by saying it was misunderstood: "I will not criticise it. If it was good enough for Robert Burns, then it was good enough for me."

Tory MSP Jamie McGrigor said: "I am a Freemason, although I'm not a good attender of meetings. It has never interfered with my MSP duties, but if Mike Russell feels it is necessary for him to resign, then it's a matter for him."

A spokesman for the first minister said: "Mike volunteered this information on his register of interests last year. I've no idea about other ministers as it isn't a declarable interest, but I do know that the first minister isn't a member."

A spokesman for the Freemasons could not be contacted.