A drop in blue-chip tobacco stocks after a report showing declining cigarette volumes and losses in pharmaceutical giants was enough to offset gains in mining heavyweights and push London's main stock index into the red on Tuesday.
The FTSE 100 was 0.1% lower, while the mid-cap FTSE 250 rose 0.4%.
British American Tobacco and Imperial Brands were among the biggest drags on the main index after data from Nielsen showed cigarette industry volumes deteriorated in the four weeks to May 18.
AstraZeneca snapped a four-day winning streak and rival GlaxoSmithKline also fell after rising for the last three sessions.
The drugmakers gave up more than 2% each, and offset a rise in miners that had capitalised on China's iron ore prices hitting record highs earlier on Tuesday.
The session's trading came against the backdrop of continued uncertainty over China's trade dispute with the United States, after US President Donald Trump said Washington was not ready to make a deal with Beijing but that he expected one in the future.
"News here, rumours there - not a lot for markets to really hang their hats on right now," Markets.com analyst Neil Wilson said.
In a news-driven move, healthcare provider NMC Health advanced 7.5% on its best day in more than six months after hiking its 2019 revenue and core earnings targets.
Brexit-sensitive stocks such as retailers, which took a hit last week ahead of Prime Minister Theresa May's announcement that she would resign, also recouped some losses.
"The UK is sort of stuck in limbo, unable to fully move forward with anything Brexit-related until the next PM is found," Spreadex analyst Connor Campbell said.
Shares of mid-cap builder Galliford, one of those to have suffered from the collapse of major government contractor Carillion last year, were up 3.6%. They had earlier surged as much as 8.2% after news emerged of a rebuffed offer for two of its units from Bovis Homes.
Tour operator Thomas Cook, hammered last week by worries over its cashflow and summer sales, climbed more than 21% on its best day since early December, after Berenberg raised its rating to "hold" from "sell", citing bids the company has said it has received for its airline unit.
"The deterioration in Thomas Cook's financial position leaves the company looking for a white knight to pay a fairly punchy multiple for the airline," Berenberg analysts wrote.