"It’s just astonishing,” smiles Amy Wadge. “Twenty years ago, I did everything to try and make a success of being a solo artist, so for all of this to happen almost without really trying has been wonderful.”

The co-writer for superstars Ed Sheeran and Camila Cabello is describing the impact of Keeping Faith, the atmospheric and emotionally tumultuous Welsh BBC One drama for which she wrote and recorded the soundtrack.

Faith’s Song, the heart-tugging ballad that featured prominently across both ...