It's emerged that two tube trains collided on the District Line in the early morning of 1 May.
The track between East Putney and Southfields stations had moved slightly, causing two trains passing in opposite directions to bump into each other. Nobody was injured but the trains were damaged and taken out of service. The line was checked and has been modified, but the RMT says "the incident once again shines the spotlight on the cuts to track inspections and maintenance at London Underground". The union also says the drivers stopped the trains and have argued once again against driverless trains.