Scottish Secretary David Mundell has refused to confirm if he will campaign for the UK to remain in the EU.
The Tory frontbencher said he would make his position known once the prime minister’s negotiations had been concluded.
SNP Westminster leader Angus Robertson raised the issue during Scottish questions in the Commons yesterday.
He asked Mr Mundell if he would personally commit to supporting the In campaign, regardless of the fact the reform package proposed by European Council President Donald Tusk has yet to be agreed by the other member states.
The Moray MP said: “The single European market and the ability to impact the legislation that governs it is hugely important to the Scottish economy – especially the exporting sectors, such as Scottish whisky.
“Will you confirm that regardless of the ongoing negotiations, you will personally campaign for Scotland and the UK to remain within the EU?”
Instead of indicating what he would do, Mr Mundell told MPs Scottish Conservative leader Ruth Davidson had expressed “exactly that position”.
Mr Robertson pressed him again for an answer, adding: “Making a positive case for remaining in the EU will be crucial in the weeks and months ahead.
“Will you give a commitment not to repeat the grinding negativity of ‘project fear’ and condemn ridiculous scare stories, such as those from the prime minister on immigration and the refugee camp in Calais?”
Mr Mundell, who has previously argued that Scotland benefits from the terms of Britain’s EU membership, replied: “I’ll make my position known when the negotiations have been concluded.”
But he also offered to share a platform with Nicola Sturgeon, Alex Salmond and Mr Robertson in the event the reform package does go ahead and if he is campaigning to keep Scotland in the EU.
The prime ministeris currently trying to convince other European leaders to get behind the draft deal, which sets out an “emergency brake” on benefits for migrant workers, as well as measures to give national parliaments more power to block EU laws.
The proposals pave the way for an in/out referendum in June, but must first be agreed at a crunch Brussels summit next week.