The suspension of trading on the London Stock Exchange (LSE) hit broking firms across the City today as dealers expecting a busy day’s work were left twiddling their thumbs.

The computer failure means that brokers will not be able to earn commissions from trades and the LSE will record losses through missed trading fees and from customers using rival platforms.

More than £7 billion worth of shares are traded each day on the LSE, through nearly 700,000 separate transactions.

It is also estimated that stamp duty on shares raises about £4 billion a year, meaning that, in theory, if all share trades went through the LSE, the Government would have lost £15.9 million today.

The only bright spot for some was that the lack of trading in shares meant that dealing in commodities, such as oil and currencies, was brisk.

David Buik, of BCG Partners, said the timing of the LSE's problem could not be worse, given the importance of the Freddie Mac and Fannie Mae bailout, combined with the increasingly fierce competition that the exchange faces.

“This is the worst day this could have ever happened; people will be very unforgiving,” he said, noting that traders around the City would feel like they had been "cheated".

The bitter feeling towards the exchange’s problems and the lack of information about when trading would recommence, if at all, reverberated around the Square Mile.

Manoj Ladwa, a trader at TradIndex, said that, given how early the failure occurred, it had drawn a line under the day and was likely to cost the group in lost trading commissions. “We had expected decent activity today but it’s difficult to say how much people will have lost,” he said.

But he said his company was busier than normal with clients that wanted to trade commodities and currencies because of their inability to deal in shares.

The trading halt is likely to have biggest consequences for the LSE, which is coming up against strong competition from other platforms.

Turquoise and Chi-X, rival share-trading systems that are backed by investment banks, were working all day without any problems and were understood to be busier than normal.

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