"We're disappointed that the RMT Union is intending to organise a [strike] ballot. We will continue to progress the constructive discussions that are taking place over this matter with the RMT and our staff representatives."
The Rail Maritime and Transport Union (RMT) is balloting its members in a row over bonus payments for staff working during the Olympics.
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Homes have been evacuated as the Army works to defuse an unexploded World War II bomb discovered near Wembley Stadium.
The strike threat came just minutes after a national rail strike planned for Monday was called off.
These breathaking views were taken from a helicopter high above the capital.