The SNP's new Westminster leader has blasted the "shambolic, rudderless" Conservative government as he pressed the Prime Minister to involve devolved administrations from different parts of the UK in Brexit negotiations.
Ian Blackford argued it was "not a question of if but when" for Theresa May about involving the governments in Edinburgh and Cardiff in the crucial talks.
He said that after the Tories lost their majority in the House of Commons in the snap General Election, Mrs May was "in office but not in power".
He spoke out as Nicola Sturgeon's SNP administration in Edinburgh continues to call for Scotland to remain in the single market after the UK exits the European Union (EU) - even though this proposal has already been rejected by Westminster.
Ms Sturgeon has also been pressing for a place in the Brexit talks, with suggestions being made that Holyrood could threaten to withhold consent for the Great Repeal Bill to try to win a place in the negotiating team.
Mr Blackford became SNP Westminster leader after Angus Robertson was ousted from his Moray seat by the Conservatives in the election, as the SNP saw its tally of MPs fall from 56 in 2015 to 35.
But after the Tories lost their overall majority, he said: "Theresa May's Tory party has been humbled and it is clear from the watered down and wafer-thin Queen's Speech that she is in office, but not in power."
Mr Blackford added: "In a parliament of minorities SNP MPs will take every opportunity to remind the Tory Government that people across the UK have rejected their obsession for a hard right Brexit that would drag us out of the single market and customs union - hitting our economy and jobs so hard.
"The Tory Brexit chaos must now come to an end.
"One year on from their disastrous referendum, Theresa May cannot escape the new reality of Brexit - there is no mandate and there is no majority support.
"If she is serious about seeking a UK-wide approach then the question of involving the devolved governments across the UK in the negotiating process is not a question of if, but when.
"The SNP Scottish Government put forward an EU paper last year and instead of meeting it with a brick wall Theresa May should now respond positively and meet with the Joint Ministerial Council to discuss and acknowledge the different circumstances and votes in different parts of the UK.
"Scotland cannot be left to the hands of a shambolic, rudderless Tory Government that threatens to negotiate away our interests.
"SNP MPs will ensure that in Westminster the UK Government is reminded of their new, humbled position and will work with others to put forward a position that seeks to protect Scotland's interests and membership of the single market."