Tesco shares have continued to fall as investors digest the collapse in its profits and uncertainty around the strategy of chief executive Dave Lewis.

Rating agencies Moody's and Fitch both downgraded Tesco's debt after the stock finished on Thursday at an 11-year low, losing around £1 billion of its market value as it disclosed a 92 per cent fall in half-year profits.

Its decline continued yesterday as the wider FTSE 100 Index headed into the red - 30.4 points lower at 6388.7 after a case of Ebola was reported in New York.

Traders are anxious about Tesco's decision not to provide full-year profit guidance. Analysts have also expressed scepticism about Mr Lewis's decision to focus on improving service and reinforcing the brand before embarking on price cuts at a time when the business is facing a growing threat from discounters Aldi and Lidl.

Tesco shares fell by another one per cent, or 2.25p, to 168.75p, with rival Morrisons also off 0.6p to 152.5p.

Meanwhile, the latest figures showing a seventh successive quarter of growth for the UK economy had little impact as the 0.7 per cent rise in GDP matched expectations. The pound was up slightly against the US dollar, at 1.61, and against the euro, at 1.27.

In the FTSE 100, publisher Pearson led the fallers' board after announcing that finance director Robin Freestone was to step down after 10 years.

Pearson, owner of the Financial Times, also published a trading update showing that sales rose one per cent for the first nine months of 2014 and saying it was "performing well competitively through a period of change and in difficult markets".

The group said it was maintaining its profits guidance for the current year but shares fell two per cent, or 30p, to 113.9p.

Travel stocks, weighed down by the Ebola threat, took a further hit, with easyJet off 13p at 143.8p and British Airways owner International Airlines Group down 0.7p to 383.3p.

Drugs firm AstraZeneca's shares were down 7p to 4327.5p after US rival Pfizer announced a share buyback programme worth $11 billion (£6.85 billion), suggesting it is not mulling another takeover tilt for Astra.

On the FTSE 250 Index, shares in TSB were 4.3p higher at 263.3p after it said it had signed up one in 10 of all people opening or switching customer accounts in the UK.

Elsewhere, Spirit Pub Company lifted 1p to 107.25p as it emerged that Magners maker C&C Group has tabled a bid proposal that could scupper Greene King's existing £750 million takeover offer.

The biggest risers on the FTSE 100 Index were Shire up 155p at 405.0p, Vodafone up 3.65p at 200.5p, Standard Chartered up 16p at 111.5p and Old Mutual up 1.2p 184.7p. The biggest fallers were Pearson down 30p at 113.9p, G4S down 6.2p at 251p, Anglo American down 32p at 130.8p and Tullow Oil down 10.9p at 494.6p.