Scotland's Brexit secretary has apologised after a remark in which he suggested Eurosceptic Conservative MP Jacob Rees-Mogg was part of an alien invasion.

Michael Russell said the joke "misfired" during exchanges with Tory MSPs Murdo Fraser at Holyrood's Finance and Constitution Committee.

The committee was discussing Scottish Government's position on the UK's draft withdrawal agreement with the European Union.

The contentious withdrawal agreement has sparked days of turmoil at Westminster, with opposition parties and many in Theresa May's own party against the deal.

She heads to a crunch European Council summit at the end of this week where she hopes to finalise the agreement and flesh out the detail of the UK's post-Brexit relationship with the EU.

Fraser pressed Russell on if he had read the full 585-page draft withdrawal document, and the cabinet secretary professed to only having skimmed it.

Russell told MSPs: "I am not a laywer. I am not going to debate or discuss the fine print of this.

"We have lawyers in this room who are more than capable of doing so and I'm sure want to do so."

"What I am familiar with is both what is in here in the draft legal declaration, and also I am familiar with the recommendations and information that's come to me from distinguished lawyers."

The Scottish Conservative MSP highlighted that Russell tweeted 23 minutes after the document entered the public domain that it was a "very poor and disastrous deal".

The minister replied: "If you have an agreement based nupon a set of red lines which will be very damaging to Scotland, which this document is, then you cannot have an agreement which is going to be good for Scotland.

"Had I proved to be wrong in that, I would have admitted to be wrong. I am not wrong."

Fraser went on to ask Russell if he believed Theresa May's deal was worse than a no-deal scenario.

"When it comes to a choice between this or alien invasion, this is better, but the reality of the situation is that both are very bad," Russell answered.

Fraser said: "With respect, alien invasion is somewhat less likely than a no-deal."

Russell retorted: "I don't know, have you seen Jacob Rees-Mogg?"

Later in the same session, Fraser's Tory colleague Adam Tomkins asked the cabinet secretary to withdraw the comment, describing it as "a rush of blood to the head" and "beneath him".

Russell said: "My blood didn't rush to my head, but if the joke misfired in any sense then of course I'm sorry about that."