* Britain's Boris Johnson seeks vote on his deal
* UK PM forced to ask for Brexit delay
* European Union plays for time
By Alistair Smout and Guy Faulconbridge
LONDON, Oct 21 (Reuters) - British Prime Minister Boris Johnson will try to put his Brexit deal to a vote in parliament on Monday after he was forced by his opponents to send a letter seeking a delay from the European Union.
With just 10 days left until the United Kingdom is due to leave the EU on Oct. 31, the divorce is again in disarray as Britain's political class argue over whether to leave with a deal, exit without a deal or hold another referendum.
Johnson was ambushed by opponents in parliament on Saturday who demanded a change to the sequencing of the ratification of the deal, exposing the prime minister to a law which demanded he request a delay until Jan. 31.
In a twist that illustrates the extent to which Brexit has strained the norms of British statecraft, Johnson sent the note to the EU unsigned - and added another signed letter arguing against what he cast as a deeply corrosive delay.
"A further extension would damage the interests of the UK and our EU partners, and the relationship between us," Johnson said his own letter, signed "Boris Johnson".
The British government insisted on Sunday the country will leave the EU on Oct. 31, and plans to put the deal to a vote in parliament later on Monday though it is unclear if the House of Commons speaker will allow such a vote.
The government has proposed a debate on the deal, according to the House of Commons order paper which says the speaker will make a statement on the proceedings shortly after parliament opens at 1330 GMT.
The EU, which has grappled with the tortuous Brexit crisis since Britons voted 52%-48% to leave in a 2016 referendum, was clearly bewildered by the contradictory signals from London.
It was unlikely that the EU's 27 remaining member states would refuse Britain's request to delay once again its departure, given the impact on all parties of a no-deal Brexit.
Sterling, which has rallied more than 6% since Oct. 10, slid from five-month highs on Monday. It hit as low as $1.2850 in Asian trading before settling around $1.2920 in London, down 0.5% on the day.
Goldman Sachs raised the probability of the United Kingdom leaving with a ratified deal to 70% from 65%, cut its view of the chances of a 'no-deal' Brexit to 5% from 10% and left its view on no Brexit at all unchanged at 25%. (Writing by Guy Faulconbridge; Editing by Toby Chopra)