Humza Yousaf has been branded “simply irresponsible” by an angry Mr Jack over his spending of taxpayer cash on Scexit papers. The Scotland Secretary urged the SNP executive to “cease” working on breaking up the UK and instead dealing with more pressing issues.

The Scottish Government published its fifth independence prospectus on Thursday which focused on citizenship but was labelled a further waste of public money. It included issues such as a different colour for passports to match up with the EU.

And now Mr Jack, left,  has written to the First Minister, as well as copying in both Deputy Prime Minister Oliver Dowden and head civil servant Simon Case, to outline his anger at this continued spending on a reserved matter. He blasted the SNP for putting its “obsession with independence ahead of pressing priorities in Scotland”.

His letter will add fuel to an ongoing row between the UK and Scottish Governments on public spending and using civil servants to push for the break-up of the UK. Calls have been made for ministers to be sanctioned for overreaching into the likes of the constitution which is reserved to Westminster.