Update: Tesco (TSCO) has fallen towards the bottom of the FTSE 100 after the latest figures from researchers Kantar Worldpanel showed the 'big four' supermarkets continuing to lose market share to discounters Aldi and Lidl.
Shares in Tesco were down 3.4% at 208.6p, towards the bottom of the FTSE 100, which rose 30 points, or 0.4%, to 7,059.
Kantar data showed sales growth of just 0.9% in the 12 weeks to 7 October, which wasn't enough to stop a fall in market shares, down from 28% to 27.4% a year ago.
Sainsbury's (SBRY) recorded the most sluggish growth of the 'big four' however, with a 0.6% rise in sales that saw its market share fall from 15.8% to 15.4%. Its shares were down 1% at 302.4p.
Aldi recorded its fastest growth since January, with a 15.15 rise in sales that swelled market share from 6.8% to 7.6%. Fellow discounter Lidl drove a 10% increase in sales that raised its market share from 5.2% to 5.6%.
'We're now heading into the all-important Christmas period where supermarkets go all out to try to get one up on the competition with big offers and new products,' said Russ Mould, investment director at AJ Bell.
'As such, Tesco's board may not be best pleased with its momentum going into the seasonal push.
'The result it somewhat surprising given how much publicity Tesco generated with its Jack's discount concept launch in late-September. Countless column inches and air time drew attention to the broader Tesco group as well as Jack's and should have acted as free advertising to help get more people into its stores.'
On the FTSE 250, Drax (DRX) rose 5.5% to 386p as the power producer agreed a deal to buy a group of Scottish power plants from Spain's Iberdrola (IBE.MC) for £702 million.
Merlin Entertainments (MERL) fell to the bottom of the 'mid-cap' index, down 8% at 340p after the amusement parks operator said performance of its Legoland business over the summer had failed to match expectations.
'Topline revenues might be moving in the right direction, but under the surface Merlin is struggling to get customers through the gates,' said Nicholas Hyett, equity analyst at Hargreaves Lansdown.
'The smaller Midway attractions have been weak for some time, largely because of terrorist attacks in London dampening the tourist market in the group's single largest destination. But the worrying thing in these numbers is that the previously strong Legoland business seems to be joining the slump.'
Among 'small-cap' stocks, McCarthy & Stone (MCS) jumped 6% to 134.9p as the government announced retirement home builders would be exempt from a cap on ground rents for new-build housing.