Obviously it was near West Drayton on the Great Western Main Line and not at Uxbridge. This isn't the first time this has happened. Usually it's the signalling that gets disrupted. The problem is that they don't know exactly where the cables are even if they think they do. The cable ducts are buried under the balast to make it harder for thieves to get at them (most are copper) and every time the track gets tamped and new ballast is tipped on top the cables get pushed a little further into the cess or down the embankment. Even if they are shown on plans they may not be where they were when the plans were drawn.
Btw what's the new measurement train got to do with it?