SNP MP Ian Blackford claimed Mrs May had “put her narrow party interest before that of the country” as he argued the week’s events had made a no-deal scenario much more likely.
Speaking at PMQs he said: “This week the Prime Minister caved into her right wing Brexiteers, undermining her negotiating position with the EU.
“In her attempt to hold together her fractured party, she’s managed to unite the country against this Government.
“Playing fast and loose with her own position makes the UK a laughing stock with her negotiating partners.
“The Prime Minister has put her narrow party interest before that of the country.”
“Is it not the case that the events of this week make a no deal much more likely?”
Mrs May defended the Government’s approach to Brexit and criticised the SNP’s support for Scottish independence.
She replied: “We are negotiating with the EU on the basis of the Chequers agreement and the white paper and those discussions have been started this week and have been continuing this week, but can I say to him also, he talks about putting a political party’s interests before that of the country.
“I think the SNP should really think about what they are doing when they promote the independence of Scotland which is clearly against the interests of their country.”
Mr Blackford argued the UK could not “crash out” of the EU without a deal as he called on Mrs May to extend Article 50.
He said: “The reality is that this is a Prime Minister that has lost control of her own party, a Prime Minister who is in office but not in power.
“A parliament which is so divided, that it simply cannot function.”
He added: “We cannot crash out of the EU without a deal, we need to think of the next generation, who will pay a price for this folly.
“They will see lost opportunities and lost jobs.
“Did the Prime Minister come into Parliament to have this as her legacy, will she now face up to the reality and extend Article 50?”
Mrs May simply replied: “No.”