The FTSE 100 Index has fallen into negative territory, slipping back from early gains made on the back of strong overnight progress in Wall Street.
Top flight shares dipped below the important 4300 mark, despite seeing the tech-laden Nasdaq move above 1,900 for the first time in 18 months on Thursday night.
By mid-morning, the Footsie stood 24.4 points lower at 4290.3, losing sight of the 12-month high it had reached earlier this week.
With little in the way of corporate news in London, dealers were expecting an uncertain session for blue-chip shares.
The expiry of quarterly futures and options contracts is also expected to make the session hard to predict.
Also losing out was Cadbury Schweppes after warning hot weather in Europe had dented confectionery sales. Shares lost 8p to 379.75p - a 2% fall.
Elsewhere, cruise operator Carnival gained 61p to 2124p in the wake of third quarter results, showing an improving trend for demand following the Iraq war.
Outside the top flight, security printer De La Rue gave shareholders a much needed boost with forecasts of significantly better half-year results than originally hoped.
The progress of an Iraqi bank note printing contract has lifted De La Rue, which surged 7% or 18.5p to 307.5p in the first hour of dealing.
But Anglo-Australian pallets firm Brambles Industries shed almost 4% or 7p to 182.25p after dismissing renewed speculation about potential takeover offers.
Also involved in takeover speculation was IT hardware firm Spirent which climbed 12% or 7p to 63.25p.
The stock trades in a sector considered ripe for consolidation by City analysts.