The FTSE 100 eked out a 0.1% gain, outperforming the broader European index, which fell on poor German economic data, and as a profit warning from Mercedes-Benz owner Daimler triggered a sell-off in the region's carmakers.
The mid-cap FTSE 250 shed 0.1%, driven in part by a weak sterling, with traders seemingly reluctant to bet on the currency until the Conservative Party leadership contest concludes.
"I think global markets generally are in a bit of a holding pattern ahead of all-critical G20 meeting," Raymond James analyst Chris Bailey said.
Investors will be watching intently on the outcome of President Donald Trump's upcoming meeting with Chinese counterpart Xi Jinping at the G20 summit in Japan, which could very well influence the course of a protracted trade war that has roiled the global economy.
Ahead of the meeting, Chinese Vice Commerce Minister Wang Shouwen said both countries should make compromises in trade talks, after negotiations broke down last month.
"The absence of confrontational rhetoric over the last fortnight ahead of G20 talks... may have enabled a higher ceiling for sentiment. Nerves remain though," Cityindex analyst Ken Odeluga said.
HSBC and Standard Chartered were among the biggest drags on the main index, offsetting advances in healthcare firms AstraZeneca and GlaxoSmithKline - considered among safer bets in uncertain times.
Admiral Group was among the biggest gainers on the FTSE 100, adding 3.2%, after Barclays upgraded the insurer's rating by two notches.
Shares of retailers and supermarket chains slipped, however, after a forecast showed consumer spending in Britain this year would grow at its slowest rate in six years.
Sainsbury shed 4.2%, Kigfisher and Marks & Spencer lost about 2.5%, and Tesco dropped 2.2%.
On the mid-cap index, power producer Drax lost 5.2% as Citigroup cut its price target on the stock and said it saw no reason to turn more constructive given the current commodity price outlook.
Dixons Carphone fell 3.7% as last week's disappointing annual results prompted further rating downgrades of Britain's biggest seller of electricals and mobile phones.
(Reporting by Shashwat Awasthi in Bengaluru; Editing by Toby Chopra)
By Shashwat Awasthi