help with identifying this warbler?

I took several photographs of this bird yesterday and I'm struggling to identify it.

It spent some time in scrub at the edge of a birch wood on the Eastern Moors in the Peak District. It wasn't calling while I watched it so that made ID a little more difficult.

There are willow warblers, redstarts, blakcaps, whitethroats & tree pipits calling in the area and there have been grasshopper warblers in that area in previous years but this bird doesn't seem to fit with any of those. A friend suggest female pied flycatcher but it looks a lot paler than the ones I've seen elsewhere and I know the song well and would be aware if they were in that area.

Thanks in anticipation...