The pound falls to the lowest level against the dollar since April 2017 after prime minister's statement.Read more
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It is not clear whether the pound will recover or fall further, says John Marley, an analyst at Smart Currency Business.
"One scenario is that May wants to avoid an embarrassing defeat... another is that she may be very close to securing agreement from the EU with further negotiation so sterling could still move either way from here," he said.
Chris Turner, head of currency strategy at ING in London, said the likely loss of the vote accompanied by the growing risk of a leadership challenge "should be negative for the pound and send EUR/GBP above £0.9000 this week".
This chart show's the pound's precipitous fall against the dollar today.
Sterling is now trading at $1.2664 against the greenback, marking a fall of half a per cent since the start of the day.
Hamish Muress, currency analyst at International payments firm OFX, says that the confusion over whether the Brexit vote will go ahead on Tuesday "provides the market [with] an insight into the chaos and disagreement within Downing Street".
"Rumours that Theresa May is set to pull tomorrow’s vote contradict those of a Downing Street spokesperson, and the fact the news was broken over a conference call instead of in a cabinet meeting speaks volumes."
He says: “Many predicted that tomorrow would be the big day for any movement in the pound. However, it has already reached three-month lows against the euro and, depending on whether the vote tomorrow goes ahead, could hit lows last seen against the dollar in August.”
Sterling has fallen 0.21% on the dollar to $1.2691, following news reports in the Daily Mail and the Sun that Theresa May has called an emergency conference call with Cabinet ministers.
Political editors for the Sun and the Daily Mail said that a decision was pending on whether to pull tomorrow's vote on her Brexit withdrawal deal.
Meanwhile, the pound has fluttered a little lower against the dollar at $1.2678.
The pound is now down 0.27% against the dollar at $1.2698.
Sterling is off 0.33% against the euro at €1.1133.
Meanwhile, BBC political editor Laura Kuenssberg tweets:
BBC political editor Laura Kuenssberg also says that there may be a statement from Brexit Secretary Stephen Barclay related top Article 50.
While she also says...
The pound is now down against the dollar at 0.49% at $1.2671.
It is 0.64% lower against the euro at €1.1098.
From a small gain early this morning, sterling is now down 0.10% against the dollar at $1.2720.
The pound is down 0.26% against the euro at €1.1141.