Legal documents establishing the Scottish Islamic Foundation (SIF) as a company were witnessed by a member of the SNP's staff at the party's Glasgow head office.

The papers relate to SIF's application to be set up as a company in May of this year. As part of the process of incorporating a company, a director must sign a form to confirm that all details are present and correct.

This document – 'the declaration on application of registration' – was signed at 50 Wellington Street, the same office which contains the SNP Glasgow HQ.

The document was then formally witnessed by Calum MacLeod, an SNP solicitor.

The new revelations over the company's close ties to the SNP come after leading Muslim figures in Glasgow publicly claimed last week that the SIF had received special treatment from the Scottish Government.

In March, the Scottish Islamic Foundation received a £215,000 grant from SNP ministers to fund a major 'IslamFest' event next year being organised by the group, and to pay for its offices in Glasgow.

The general secretary of the Glasgow Islamic Mosque, Dr Shafi Kauser, said: "This is about scratching their own backs."

Mohammed Asif of the Scottish Afghan Society added: "The First Minister is just helping his own members."

The company is being run by chief executive Osama Saeed, a former researcher for the First Minister, and an SNP member who is fighting to become an SNP MP in the Glasgow Central constituency.

Saeed is campaigning to win support within Glasgow Central's large Muslim population. He intends the publicly funded Scottish Islamic Foundation to be "a platform" for the views of Muslims.

But an executive member of the Glasgow Mosque, Ghulam Rabbani, added to the Muslim voices in Glasgow opposing the funding package last night. "Nobody knows this organisation (SIF] in the Muslim community," he said. "I think they have got money because he was employed by Alex Salmond."

Meanwhile, opposition party members who had appeared to back SIF have started to express concerns at the arrangement.

Labour MSP Pauline McNeill attended the launch of SIF last month and has been used to claim the SIF has cross-party support. She said: "I attended the launch of the SIF along with the other political parties and church leaders and we were asked to say a few words. But speaking at an event is not an endorsement of the Government's recent decision to fund SIF and not other organisations established in the field. Ministers need to explain why this decision is appropriate."

David Mundell, shadow Scottish secretary, added: "Whilst we are very supportive of the principle of this sort of enterprise, concerns have been raised with us about the organisation."

However, the Scottish Government hit back last night, insisting the funding for the SIF was made "after the normal process of value for money evaluation".

The spokesman added: "This remains a non-story. The important thing is that IslamFest will be a fantastic cultural as well as commercial opportunity for Scotland as a whole, as well as our Muslim community, carrying cross-party and indeed interfaith support.

"All funding applications to the Scottish Government are scrutinised and are considered for their match with Government priorities and assessed for their value for money."

Scottish Government sources hit back against the cronyism claims by claiming that the funding deal for the IslamFest had been agreed "in principle" by the previous Lib-Lab Scottish Executive. A source close to Salmond said: "Any attempt by opposition parties to play petty politics on this will backfire, particularly given that it was the previous administration that first agreed to provide funding for Islam Fest."

A Scottish Executive spokeswoman also confirmed that Salmond had contacted the chairman of Glasgow Central Mosque Bashir Maan last Saturday as claims began to surface that the SNP had turned them down over an application for funding.

The claims had been made by other leading figures at the mosque, including the general secretary, who told this newspaper that they had "heard nothing" from the SNP over their own application for funding, in contrast to the SIF's deal.

Subsequently, a statement in Maan's name was issued by the Scottish Government later that day in which Maan insisted that the application had not been turned down and was still live.

A spokesman for SIF pointed out that the offices of the company are at a different location. "The Form 12 witness is not an honorific position, and the location of witnessing irrelevant," he said.

A spokeswoman for the Scottish Government said she could not say whether the company papers had been signed in the SNP's office, as 50 Wellington Street contains several offices.