Ian Blackford has accused Theresa May and Jeremy Corbyn of cooking up a "backroom deal" by holding cross-party talks on Brexit.
Speaking during Prime Minister's Questions, the Scottish MP said there was "no such thing" as a "good Tory-Labour Brexit deal".
"People can't have faith in a backroom deal cooked up by two leaders who don't possess the ingredients to hold their parties together, never mind hold these islands together," Mr Blackford told the Commons.
"The Prime Minister must recognise the difference between what she believes is duty, but what the rest of us see as delusion."
His comments followed last week's announcement that the Prime Minister and Labour leader would meet to find a way through the Brexit impasse.
Hitting back at the MPs comments, Mrs May said: "It's a little difficult for many of us in this House to hear him week after week stand up and say the UK should stay in the EU, when Scottish Independence would have meant taking Scotland out of the EU."