The FTSE 100 was up 0.7 percent, outperforming its euro zone peers. The FTSE 250 was 0.2 percent higher.
GVC led the blue-chip gainers after it reported a surge in net gaming revenue, and Hargreaves Lansdown analyst George Salmon said the gambling firm's digital division remained GVC's "trump card" amid regulatory changes in the industry.
The stock jumped 7.1 percent, its best day since mid-December.
Vodafone, the world's second-largest mobile operator, gained 2 percent after saying it intends to raise about four billion euros by issuing mandatory convertible bonds.
Companies with a larger international presence, such as Unilever, Reckitt Benckiser and AstraZeneca found support from the pound, which fell on profit-taking.
Sterling's weakness came as Britain's opposition Labour Party's spokesman was quoted as saying few Labour lawmakers would back Prime Minister Theresa May's Brexit deal in a parliament vote this month.
Capping the gains on the index was industrial firm Intertek, which slipped 3.7 percent. A trader attributed the fall to profit-taking after the company's results.
Another notable faller was Royal Bank of Scotland, dipping 2.4 percent after the Bank of England said the EU's financial services sector would face disruption in a no-deal Brexit scenario with some spillover in Britain.
"The very fact that they are talking about the possibility of a no deal is a bit of a worry. The EU may well be the biggest loser of a no-deal Brexit, but it is also implied that the UK would lose as well," CMC Markets analyst David Madden said.
He pointed out that RBS was relatively more domestically-focussed, which would leave it more exposed to potential hits from a no-deal Brexit.
Sainsbury's also fell 1.2 percent as data from Kantar Worldpanel showed the supermarket chain was the worst performer of Britain's big four supermarket groups in the latest 12-week period.
On the mid-caps, aviation services provider BBA Aviation skidded 8 percent after annual results, while Ted Baker, whose founder Ray Kelvin quit on Monday after allegations of misconduct, fell 3 percent.
Specialty chemicals company Elementis dropped 8 percent after saying global market conditions remained challenging in 2019. That took the focus off its 2018 results which showed profit and revenue rose.
Struggling department store group Debenhams ended 2.8 percent lower after slumping as much as 12 percent as it withdrew its full-year outlook and said talks with stakeholders to restructure its balance sheet would likely be disruptive.
(Reporting by Shashwat Awasthi and Muvija M in Bengaluru; editing by Josephine Mason and Janet Lawrence)
By Shashwat Awasthi and Muvija M