Chi-X Europe criticized the London Stock Exchange
The LSE's main rival said the exchange put its market into auction status when the system broke down and that this triggered the block on routing to other venues.
The auction status hampered investors' ability to trade by not enabling participants to seek a reference price on another venue, multilateral trading facility Chi-X said in a statement.
A spokesman for the LSE denied Chi-X's claim.
Our decision was a result of customer feedback, he said. Some were experiencing connection issues while others were not, and customers requested for the market to be put into auction status so that there would be a level playing field.
Chi-X said many firms' trading systems treated the auction status like a normal market event such as the daily closing auction.
By contrast, on November 9 the LSE halted trading during a partial systems failure, and many member firms were able to switch to other venues to trade UK stocks, Chi-X said.
We call for the LSE and any other market of listing to close their market outright when outages occur in order to allow market participants to continue trading, the statement said.
Chi-X also called on the Financial Services Authority to ensure the continuation of trading and an orderly market.
Another LSE rival, Nasdaq OMX called for standardization of market data in Europe.
This would enable trading to continue even if one market fails to operate, said Charlotte Crosswell president of Nasdaq OMX. We are supportive of the European Commission further investigation this issue.
(Editing by Will Waterman)