The pound fell on Monday as a debate in Britain's parliament exposed the level of dissatisfaction within British Prime Minister Theresa May's governing Conservative Party over her plans for Brexit.

The pound fell to an intraday low of $1.3223 on news that May had bowed to pressure from Brexit supporters and accepted their changes to a customs bill that underpins Britain's exit from the EU.

"The move in sterling is pretty contained at this point but this [accepting of amendments] is being viewed by the market as a step towards a leadership contest," said Jordan Rochester, currencies strategist at Nomura.

Eurosceptics say May's plan leaves Britain too close to the European Union and are trying to force her to change course, while pro-EU Conservative lawmakers say it leaves the country too distant from its biggest trading partner.

Sterling has struggled to capitalise in recent weeks on signs that the economy is improving because of mounting uncertainty over whether Britain can secure a trade deal with the EU before it leaves the bloc next March.

Markets expect the Bank of England to hike interest rates in August but the British currency has fallen 9 percent since April partly because of the wrangling within May's party.

May is expected to survive Monday's debate on a customs law but the debate risks undermining the government and increasing the chances of an early election which would hurt the pound.

"Political uncertainty helps to explain why the pound has not strengthened yet on the back of the government's plans for a softer Brexit," said analysts at MUFG.

At 1545 GMT the pound was down 0.1 percent versus the dollar at $1.3224 and down 0.3 percent against the euro at 88.52 pence. .

Sterling finished last week down one percent against the dollar, its biggest weekly drop since late May.

President Donald Trump's visit to the UK last week added to uncertainty about the Brexit talks and Britain's trade relationship with the United States after the divorce. Trump criticised May's handling of the Brexit talks.

May attempted to face down would-be eurosceptic rebels by warning on Sunday that if they sink her premiership then they risk squandering the victory of an EU exit that they have dreamed about for decades.

Meanwhile over the weekend, German business groups told members to prepare for a hard Brexit.

Long bets on sterling have been whittled down in recent days with overall net positions mildly bearish on the currency, positioning data shows.

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