Sterling fell today and was headed for a fourth consecutive week of losses as British Prime Minister Theresa May pressed ahead with plans for a parliamentary vote on her Brexit deal with the European Union. 

Sterling's near-term fate hangs on whether May can win a majority for her Brexit deal in a vote on December 11 that will define Britain's departure from the EU scheduled for March. 

The odds look stacked against her getting the deal through a deeply divided parliament. 

The pound was down 0.4% at $1.2746 today, near an 18-month low of $1.2659 hit on Wednesday. It also weakened 0.3% against the euro to 89.27 pence. 

The Times newspaper reported yesterday that senior ministers were urging May to delay the vote for fear of a rout but her spokesman has said it would go ahead as planned. 

A defeat on Tuesday could open up a series of different outcomes to Britain's departure from the EU - each with its own impact on sterling - ranging from leaving without the deal to holding a second referendum on membership.

The growing chance of averting Brexit altogether - potentially via a second referendum - has led some investors to start pricing out the prospect of a damaging "no deal" departure from the EU, analysts say.