During that debate, from which former Scottish Tory leader Ruth Davidson was also absent, the Conservatives were the only party which did not back a vote to oppose under any circumstances a no deal Brexit.
Mr MacDonald’s immediate local concern is uncertainty of the future of Ineos’ petrochemical plant at Grangemouth amid UK Government plans to introduce zero tariffs - still to be fully spelled out - which the firm itself says would compromise its trading position.
Scottish Government Derek Mackay aims to press the UK government for assurances on the Grangemouth plant’s future.
However today’s explosive tweet from Mr Tomkins has focused SNP attention on “Tory splits”.
Mr Tomkins, who has been touted as a possible successor to Ruth Davidson as Scottish Tory leader, said: “If the law compels the PM to act in a certain way, and if the PM refuses so to act, he has only one option: to resign his ministry. It really is as simple as that.
“Irrespective of what we think about Brexit, or the PM, surely we can all agree on one fundamental principle: the government is bound to obey the law”.
SNP Westminster Deputy Leader Kirsty Blackman MP said: “Boris Johnson must make clear he will respect the law, respect democracy, and take the threat of a catastrophic no-deal Brexit off the table. If he cannot - he must resign.
“With Westminster in crisis and Tory splits deepening, the question is - if the Prime Minister’s own party cannot tolerate his government why should Scotland be expected to?”
Mr Tomkins’ concerns were in contrast to a tweet he made yesterday, which enquired which side former First Minister Alex Salmond would be supporting in the Scotland v Russia game (which Scotland lost).
Earlier this week thousands of residents in Falkirk’s two UK parliamentary constituencies signed a petition calling for the highly controversial suspension of Parliament to be lifted.#
Linlithgow and East Falkirk had the most signatures, 2,155, followed by Falkirk with 1,901.