Things just got serious for the U.K. and the EU. 

The British Pound slid to a 3-year low against the euro and a 3-month low versus the dollar on Monday, after a March deadline was set for the start of the formal process that will split Britain from the European Union.

Britain's Prime Minister Theresa May told her Conservative party's annual conference on Sunday that she was determined to move on with the process and win the "right deal", in a move to ease fears inside her party that she may delay the divorce.

Triggering Article 50 of the EU's Lisbon Treaty will give Britain a two-year period to clinch one of the most complex deals in Europe since World War Two, and will redefine the country's ties with its biggest trading partner.

The GBP, having just posted its worst run of quarterly losses since 1984, slides more than 1% against the USD to $1.2845 GBP=D4. That left it less than half a cent away from the 31-year low it plumbed in early July, shortly after the shock June 23 vote to leave the EU.

The pound also shed 1 percent against the euro to hit 87.48, its weakest since August 2013.

Elsewhere, risk sentiment benefited from news that Deutsche Bank was attempting to negotiate a much smaller fine with the U.S. Department of Justice, though no formal settlement has been announced yet.

The EUR edged down 0.1 percent to $1.1237, remaining well above Friday's low of $1.1153 hit before hopes of a reduced Deutsche settlement pulled it higher.