The FTSE 100 was 0.1 percent lower by 0721 GMT, while the more domestically-focussed FTSE 250 added 0.3 percent as the local currency strengthened.

Prime Minister Theresa May, after seven hours of cabinet meetings on Tuesday, said she would seek another Brexit delay beyond April 12 to try and agree a European Union divorce deal with the opposition Labour leader.

Although the default remained that Britain would leave the bloc without a deal, her move offered the prospect of keeping the UK in a much closer economic relationship with the EU after Brexit.

That boosted shares in housebuilders and British banks including Lloyds and Barclays.

But exporters felt the brunt of a stronger sterling. British American Tobacco, spirits giant Diageo, GlaxoSmithKline and Unilever were the biggest drags on the main bourse.

Burberry was the biggest blue-chip faller with a 3 percent drop as JP Morgan analysts slashed annual core profit estimates for the luxury goods brand on Brexit-related sterling volatility.

Transport company Stagecoach surged 11 percent, topping the midcaps, after it hiked its full-year adjusted profit target on what it called "strong trading and positive progress" in the UK rail business.

The small-cap index saw some big fallers with Superdry slumping another 9 percent on news that its co-founder and former boss Julian Dunkerton was appointed interim CEO after winning the backing of shareholders to join the board by a slim margin.

CMC Markets slid 7.4 percent as it forecast a plunge in net operating income for fiscal 2019 as new rules curbed client trading activity and announced the departure of its CFO.