There are plenty of cases in recent electrification where stretches of double track line use twin-track cantilevers (TTCs) on one side with no masts on the other side.
Typically they occur on the inside of curves, or in areas where ground conditions are poor or access is difficult on one side of the track.
In TTC territory you can usually glimpse the cantilever overhead from the other side of the track, but it can be problematic getting the full picture of masts and wiring in those areas.
There are plenty of TTCs on the Leeds-Morley section too, as the line weaves round the hills.