Sterling was mixed in afternoon trading, as excitement over the official trigger of Article 50 waned.
The pound, which rose 0.6% against the euro earlier in the day, was only up 0.1% versus the euro at 1.153 by the late afternoon.
The UK currency fell further into the red against the US dollar, down 0.4% to 1.240.
The FTSE 100 ended the day higher by 0.4% to 7,373.72, thanks in part to the weaker pound.
It came after the Prime Minister Theresa May sent a letter to European Council president Donald Tusk, formally triggering the two-year process of UK withdrawal from the European Union.
Neil Wilson, a senior market analyst at ETX Capital said: "The countdown to Brexit has begun but by and large markets shrugged off the triggering of Article 50.
"Stocks and the pound took the momentous decision in their stride, largely as expected as Brexit was already priced in.
"We might have expected a touch more volatility as the UK delivered the letter but markets were pretty calm."
However, Mr Wilson said Britain should brace itself for a long period of volatility from the pound as the Government embarks on its "hugely challenging" Brexit negotiations.
"A truly hard Brexit has not been priced into sterling. We could see it move lower still if negotiations take a sour turn - 1.10 US dollar is feasible."
Sterling has slumped 17% against the US dollar and 15% versus the euro since Britain voted to leave the European on June 23.
Across Europe, Germany's Dax and French Cac 40 both rose around 0.4%.
The price of Brent crude oil climbed 1.7% to 52.21 US dollars a barrel (£42.10) as armed protesters blocked the western Libyan oil fields of Sharara and Wafa, disrupting supply.
In UK stocks, London Stock Exchange Group was one of the biggest risers, up 2.7%, after European regulators torpedoed its £21 billion merger with Deutsche Borse, saying the two exchanges failed to address competition concerns.
The move comes after the LSE rejected the commission's request last month to offload its 60% stake in the Italian trading platform MTS.
Mining giant BHP Billiton was close behind - rising just under 2.7% - after saying it was well positioned to boost value and returns from its western Australia iron ore operation.
In a contrast of fortunes, travel giant Tui Group sank 1% despite summer holiday bookings meeting expectations.
The Thomson owner said British sun-seekers were snapping up more long-haul holidays as concern over terrorist attacks and political turmoil continue to blight markets in Turkey and North Africa.
Away from the top tier, Flybe Group shares slipped 1.1% The airline said profits would take a £5 million to £10 million hit due to a major systems upgrade designed to bolster online sales and improve customer experience.
It comes as the company struggles with slowing demand and a spate of cancelled flights.