The SNP's Westminster leader Ian Blackford has been forced to withdraw a comment accusing Theresa May of being a "liar" in the House of Commons.

He risked getting thrown out of the chamber as he shouted the remark from the SNP frontbench after the Prime Minister said economic analysis of her Brexit proposals had been carried out.

MPs are not permitted to accuse other parliamentarians of dishonesty in the chamber.

The tense exchanges came as May was updating MPs on Brexit ahead of the next series of Commons votes on EU withdrawal.

The Prime Minister restated her plan to put forward an amendable motion for debate on Thursday, with the possibility MPs could table further amendments seeking Brexit alternatives.

Votes on amendments in late January saw Parliament reject measures like delaying Britain's exit from the EU by extending Article 50 and giving MPs more control over the Brexit process.

Addressing the Commons prior to his outburst, Blackford said May was living in a "parallel universe" and "lost in a Brexit fantasy".

He called on the Prime Minister to publish specific economic analysis on her EU withdrawal deal.

The UK Government published impact assessments on various Brexit scenarios last November, but the analysis did not attempt an exact forecast on the impact of May's deal, which had only been agreed with the EU two weeks earlier.

"He talked about the economic analysis. We did publish an economic analysis of the proposals the government had put forward," May replied.

Blackford could be heard shouting: "That's not true."

In rowdy Commons scenes, Speaker John Bercow urged calm, saying there was "plenty of scope for disagreement about what is true and what isn't true".

The Prime Minister went on to suggest the SNP MP "may have inadvertently misled the House on this matter".

She was forced to sit down again amid renewed uproar, with the Speaker eventually establishing that Blackford had called May a "liar".

Bercow said: "If a member on the frontbench used that word - I'm sorry, I'm not debating it, I'm not arguing, I'm not negotiating - that word must be withdrawn at once...

"I'm advised, I think on good authority, that word was used by the leader of the Scottish National Party.

"If so... I simply ask the right honourable gentleman to withdraw that word.

"He cannot accuse another member in this House of dishonesty."

Blackford rose to tell the Speaker: "In courtesy to yourself, I withdraw."