PURSUING the Brexit Bill without the consent of the UK’s three devolved legislatures is an “unprecedented attack” on devolution and should be stopped, Ian Blackford told Boris Johnson in acrimonious exchanges in the House of Commons.

But, during a noisy PMQs, the Prime Minister appeared prepared for the expected intervention after the House of Lords the night before had defeated the Government on the Brexit Bill, backing a move - by just four votes – to underline Westminster’s commitment to the so-called Sewel Convention, which states the UK Parliament "will not normally" legislate for devolved matters without the consent of the devolved legislatures affected.

The SNP leader called on Mr Johnson to “reinstate the Sewel Convention,” telling MPs: “Devolution is under attack from this Tory Government. Powers are being grabbed back to Westminster. There is no respect for the people of Scotland, for Wales and Northern Ireland, their governments or their decisions. Yesterday, the Welsh Assembly became the third devolved parliament to refuse consent for the Tory Brexit Bill.

“Why is the UK Government ignoring the principle of consent for our national government?” he asked.

The PM responded by saying Mr Blackford knew full well there was no part or implication of the Sewel Convention to “break up the oldest and most successful Union in the world”.

The Nationalist leader, to cries of “exactly” from his SNP colleagues, insisted Mr Johnson was ignoring the principles of the Smith Commission, that is, that it was up to the people of Scotland to determine their future.

“The Prime Minister just doesn’t get it. This is an unprecedented attack. Scotland said no and we meant it,” declared Mr Blackford to expressions of disbelief from the Tory benches.

Arguing the UK Government did not have the legislative mandate to pursue its Brexit Bill, he said: “As the benches opposite bray, it’s clear that this place simply doesn’t accept the reality that the Scottish Parliament speaks for the people of Scotland. The devolution settlement must be respected.

“Prime Minister, all three parliaments and even the House of Lords have called on you to end your Government’s attack on devolution. Will he stop the attack on our parliaments?”

READ MORE: PMQs recap: Ian Blackford and Prime Minister clash over indyref and Scotland's education

But Mr Johnson picked up on his opponent’s reference to people saying no. He told MPs: “I agreed for a second with him when he said Scotland said no and it meant it and he was right,” he exclaimed to Tory cheers.

“The people of Scotland said no to independence in 2014 and they meant it because they were told it was a once in a lifetime vote by Alex Salmond and his protégé Nicola Sturgeon, and indeed by him. They were told it was a once in a generation event. The people of Scotland did it because they know full well that £9 billion comes from the UK to Scotland, 60 per cent of Scotland’s trade is with the rest of the UK and they can see the vast investments in manufacturing that comes from the UK to Scotland, whether it’s in Rosyth, £1.5bn in building fantastic ships, or at Govan, fantastic investments in manufacturing.

“We support manufacturing in Scotland; they support nothing except manufacturing grievances and they know it,” he added to shouts of “more!” from the Conservative benches.

Later, Mr Johnson launched another attack on Scottish independence after the SNP’s Angus Brendan MacNeil raised a point about Brexit.

The MP for Na h-Eileanan an Iar noted how Brexiteers might be cheered by the prospect of a “cave-in” trade deal with the US, which could raise GDP by 0.2 per cent and with Australasia by 0.02 per cent but he warned that any such agreements would only claw back one third of what would be lost by Britain leaving the EU’s single market and customs union.

READ MORE: Iain Macwhirter: Scotland could rejoin the EU, but would it want to?

He called for a published assessment of what the PM’s “breezy gambling deals” might cost for UK manufacturing from car making to food and drink.

But Mr Johnson had a ready response and returned to the subject of Scotland and independence, saying: “I might take him more seriously if he would deal with the fact that Scotland’s trade is 60 per cent with the UK.

“His proposals for a break-up of the United Kingdom would necessitate a border at Berwick and he is proposing that the pensioners of Scotland should have their assets denominated in a new currency whose name they cannot even specify.”