BT Group shares lost 24% of their value today after the telecoms giant reported a major blow to earnings at its global services division.
The company also ruled out an increase in its half-year dividend, causing shares to slide 33.9p to 108.2p.
The wider market was also under pressure after recent gains, with the FTSE 100 Index down 72 points at 4219.6 by mid-morning.
In a dramatic session for corporate news, Barclays shares initially jumped 10% after it said Middle Eastern investors were pumping up to £7.3bn (€9.3bn) into the business. The move will enable Barclays to avoid calling on taxpayer funds to strengthen finances weakened by the credit crunch.
But shares remained volatile and were later 9% down – off 18.55p to 186.7p – as a result of fears about the cost of the financing terms.
Other banks were also dragged lower, with HBOS down 2.5p at 91.5p and HSBC off 62p at 718p.
BSkyB was another stock to surrender early gains, even though it topped City expectations by revealing it added 87,000 new customers in the three months to September 30. Shares opened 3% higher but were later 2% or 7p down at 371p.
Centrica shares were down 17p to 289.25p, a drop of nearly 6%, after the British Gas firm announced a £2.2bn (€2.8bn) rights issue to pay for the potential acquisition of a 25% stake in British Energy.
The biggest riser in the FTSE 100 Index was Friends Provident after the insurer posted a 14% drop in new business sales but said it had no need to raise extra capital. Shares were 3p higher at 69.7p, despite dropping plans to sell wealth management unit Lombard.
Retailers were under pressure after department store chain John Lewis reported a 9.8% drop in sales for last week. Next and Marks & Spencer will present trading updates next week and were down 66p to 1028p and 8.5p to 222p respectively today.