The FTSE 100 rose 0.3 percent by 0959 GMT and the FTSE 250 was up 0.1 percent. The midcap gains were limited by a plunge in medical-device maker ConvaTec's shares after its disappointing results.

Investors also awaited the latest parliamentary debate later in the day on Prime Minister Theresa May's Brexit plan.

"The fact that there will now be another meaningful vote on Feb. 27 has taken the pressure off today's vote ... but Theresa May's `my deal or no deal' doesn't look like it will make it into next month," London Capital Group analyst Jasper Lawler said.

Blue chips got their biggest boost from AstraZeneca, which rose 4.2 percent to put it on track for its best day since early November. Its fourth-quarter sales beat expectations and it forecast sales growth for 2019.

Micro Focus led the blue chips, as its shares jumped 14.2 percent to their highest in nearly a year after it reported annual pro-forma revenue fell less than expected.

Investors were also digesting data showing China's exports unexpectedly increased while imports fell less than expected in January. A report that US President Donald Trump might extend a March 1 deadline for imposing higher tariffs on Chinese goods also helped the mood.

Underperforming the main bourse was Coca Cola HBC, which slipped 4.6 percent after it warned economic growth would slow in many of its markets this year. Shares were on track for their worst day in three years.

The mid-caps saw steep, news-related moves as well.

ConvaTec was the biggest drag on the index after reporting lower annual operating profit.

Frankie & Benny's owner Restaurant Group skidded 11 percent on news its chief executive officer will step down due to "extenuating personal circumstances".

Ashmore's shares slumped 7 percent as the chief executive and majority owner of the emerging-market-focused fund manager revealed plans to sell down his stake, overshadowing a rise in assets under management.

But drugmaker Indivior rose 9 percent to the top of the midcap index after its full-year operating profit jumped, thanks mostly to cost cuts.

Moneysupermarket.com added 5 percent after it said it was confident of delivering market expectations for the year and also announced a chairman transition.

Lloyd's of London insurer Lancashire was 4 percent higher after it swung to a profit in 2018 from a loss a year earlier, helped by a rise in gross written premiums.