Trading ground to a halt on the London Stock Exchange (LSE) for several hours today after its electronic trading system was hit by a major technical hitch.

Shortly after 10.30 this morning the exchange announced all FTSE 100 and order-driven securities had been placed in auction.

This meant traders could post their buy and sell orders for particular shares but could not actually execute them.

Rival trading systems like Chi-X and BATS were unable to pick up the business lost on the exchange because they rely on the LSE to set share prices.

Dealers said they were left sitting on their hands unable to trade in all but the smallest stocks.

The LSE said the crisis also meant real-time indices including the FTSE 100 indicator of leading shares couldn't be properly updated.

The exchange said it had been hit by "connectivity" problems which meant not all brokers were able to link into its electronic order book.

This is the second time this month trading has been hit on the LSE, but by far the worst failure in recent history was in September last year at the height of the banking crisis when dealing was halted for seven hours.

The LSE recently bought Indian technology company MillenniumIT in order to improve its electronic trading platform.