Commodity stocks weighed on the FTSE 100 Index as oil prices tumbled, signalling investor disappointment over reports that Opec had failed to agree to deepen production cuts to fight the global glut.
Oil prices were down more than 3% in afternoon trading at 52.12 US dollars per barrel (£40.22), sending BP down 5.4p to 473.1p and Royal Dutch Shell's 'B' shares down 11p to 2,161p.
It dragged on the FTSE 100, which ended the day flat, up only 0.04% or 2.81 points at 7,517.71.
Markets were reacting to reports from the Opec meeting in Vienna suggesting that oil production cuts first introduced in January had been extended, but not deepened, raising fears that oversupply would continue.
An official statement from Opec was pending.
Neil Wilson, a senior market analyst at ETX Capital, said: "Opec members had a chance today but bottled it.
"A nine-month extension just isn't enough to really lift oil prices as we'll continue to see US shale fill the gap. Having said they'd do whatever it takes, Opec is looking a bit toothless now.
"Instead of deepening cuts, they are continuing to tinker at the margins by curbing production by around 1.8 million barrels per day along with several non-Opec members.
"It also looks like no new non-Opec members are joining the curbs, which would have helped."
Data showing a downward revision to UK gross domestic product (GDP) growth from 0.3% to 0.2% for the first quarter of 2017 sent sterling into the red.
Economists had been expecting GDP growth to slow from 0.7% in the fourth quarter of last year, but they had pencilled in growth of 0.3% for the first three months of 2017.
Across Europe, the French Cac 40 and German Dax ended the day down 0.08% and 0.17% respectively.
In UK stocks, Daily Mail and General Trust shares tumbled 51.5p to 700.5p after posting an 11% fall in underlying half-year operating profits to £100 million and saying revenues would be lower than expected in its information business.
Pets at Home rose 3.4p to 164p after reporting a 5.8% jump in annual pre-tax profits to £95.4 million, off the back of 7.2% growth in sales to £834 million.
Petrofac plunged by a whopping 184.2p to 430.8p as the oil services firm suspended its chief operating officer Marwan Chedid following a corruption and bribery probe by Britain's Serious Fraud Office.
Halfords jumped 11.4p to 370.2p as investors focused on a 3.9% rise in retail sales in the 15 weeks to April 28, pointing to a small recovery following a 1.2% drop in like-for-like retail sales in the three months to March 31.
The biggest risers on the FTSE 100 were 3I Group up 31p to 871.5p, easyJet up 36p to 1,380p, Royal Mail up 9.1p to 438.1p, and Tesco up 2.8p to 186.75p.
The biggest fallers on the FTSE 100 were Anglo American down 26.5p to 1,057.5p, DCC down 110p to 7,410p, Experian down 20p to 1,646p, and BP down 5.4p to 473.1p.