The benchmark FTSE 100 Index remains below the opening mark in London after being stalled by overnight comments from the US Federal Reserve.
By mid-morning top flight, shares lingered in negative territory at 4057.7, a 10.2 point fall.
Market confidence has been knocked on both sides of the Atlantic after the Fed further trimmed US interest rates - but only by 25 basis points to 1 per cent, rather than the 50 basis points that many investors had hoped for.
But it was the Fed's warning of possible deflation in America which took its toll, sending the Dow Jones 98 points lower overnight.
Back in London, dealers warned the Footsie could test the important 4000 barrier if fresh nerves about global economic recovery set in.
There was little in the way of major corporate news to lift shares.
Retail companies enjoyed another positive start after propping up the Footsie on Wednesday.
Supermarket chain Sainsbury's gained 5p to top the Footsie risers at 261p. Tesco was close behind with a 2.75p rise to 217.75p and takeover target Safeway edged 2.75p higher to 259.25p.
On the downside, building materials group Hanson fell 7 per cent or 28.5p to 340p after warning first half profits would be lower than last year due to higher pension costs and currency translation.
Outside the top flight, housebuilder Berkeley welcomed slowing housing demand as it unveiled a near 13 per cent rise in annual pre-tax profits. Shares rose 16p to 736p.