Prime Minister May was taking questions during PMQs when SNP MP Ian Blackford asked her a question about economic analysis on Brexit and the impact of Britain leaving the single market.
But Mr Blackford got more than he bargained for when Mrs May came back with a savage retort about the state of the Scottish economy.
Mr May replied: “The Honourable Gentleman asked me for economic analysis.
“Well I’ll give him some economic analysis.
“We saw the figures this morning for GDP growth in Scotland.
“In the third quarter GDP in Scotland grew by 0.2 percent in the rest of the United Kingdom, it grew by 0.4 percent.
“Over the last year GDP in Scotland, under an SNP government in Scotland grew by 0.6 percent, in the United Kingdom as a whole it grew by 1.7 percent.”
Mrs May pointed out that with those figures, the UK was better with a Conservative government than an SNP one.
She said: “My economic analysis – 1.7 percent is higher than 0.6 percent, you’re better off with a Conservative government than an SNP one.”
Her response was met with cheers from her party.
The SNP has been leading the charge for the UK to retain its single market membership after Brexit, calling on other opposition parties to join them.
Nicola Sturgeon insisted that a new report released on Monday would prove that the UK will be better off in the EU-controlled single market and customs union instead of breaking free.
The economic impact assessment was used as ammunition by SNP’s leader in Westminster Ian Blackford in PMQs.
Ms Sturgeon said: “The Scottish Government is absolutely clear that, if the UK is indeed leaving the EU, then it must stay within the single market and customs union to prevent needless job losses and cuts in living standards.”
The Scottish First Minister branded the Prime Ministers decision not to launch her own impact assessment a “dereliction of duty” ahead of the public announcement.