Wood Warbler with two rings

Annual leave. Yippee. Went for a long hike from Soar y Mynydd down Cwm Doethie and back up through Dalar Wen, which lies above Llyn Brianne. I drove over to Soar listening to Frank Sinatra. For Frank, weather-wise it was "such a cuckoo day." Alas, not so for me. Last year on this walk I heard 5 but only 2 today and I couldn't locate a Common Sandpiper at Soar either. On the other hand "resident" birds such as Stonechat, Reed Bunting and Yellowhammer seemed present in similar numbers. I heard 12 Wood Warblers in Dalar Wen and counted 38 Whinchats in total (23 in Cwm Doethie), seemingly a big increase from last year.

I had good views of a Wood Warbler in Cwm Doethie which was carrying two rings and I wondered if anybody reading the blog might know where it could have been ringed and by whom. On its left leg it seemed to have a grey(metal?) ring, whilst on its right leg it carried a plastic ring the upper half being red and the lower half coloured royal blue. I imagine that not too many Wood Warblers are ringed but perhaps I'm wrong. If anyone has any ideas I'd love to know more.