Traders are braced for a nervous morning on Thursday after the London Stock Exchange's much-vaunted high-speed trading system ground to a halt on Wednesday afternoon, forcing the exchange to wipe clean its electronic price display system and leave part of its daily closing auction incomplete.

The outage happened just before 4pm yesterday - 30 minutes before market close and typically one of the busiest periods of the day. It meant traders were left for nearly three hours without reliable prices for the key FTSE 100 and all the exchanges' indices. The glitch - the exchange's first since early 2000 - left share traders unsure how much business had been lost and questioning how the market, Europe's largest, will open today. Although the LSE had last night identified the cause of the problem it was unable to explain how it had happened.