According to the seven judges that decided on the UK Government's appeal regarding allowing the MPs to vote regarding invoking article 50:
The Sewel Convention has no legal force. Holyrood’s legislative powers can be over-ridden as and when the UK Government chooses.
David Mundell said this in May 2016:
"The permanence of the Scottish Parliament is now written in law, as is the Sewel convention, which states that the UK Parliament will not normally legislate in devolved areas without the consent of the Scottish Parliament".
Is it safe to assume that either the only Conservative MP in Scotland was ignorant, or not telling the truth?
At least now we know that when any of the #toryelectionfraudsters say Holyrood is a powerhouse parliament, that is a complete lie.