Perhaps all the engineering work taking place outside Paddington Station today? I crossed Hampden Street footbridge (near Westbourne Park) and saw one engineering train carrying track and another engineering train of ballast hoppers and several road-rail vehicles at work, on the (north) tracks nearest the future Crossrail tracks. Not sure what they were doing.
I was surprised they weren't working on the opposite (south) side of the formation, where in recent years I had thought the tracks/sidings were disused, but have been relaid in recent months. Again I'm not sure what's happening.