Give a stream of consciousness and then the final answer. "Say You Wo n't Let Go" is a song by British singer and songwriter James Arthur. The song was released as a digital download on 9 September 2016 in the United Kingdom by Columbia Records as the lead single from his second studio album Back from the Edge (2016). The single peaked at the top of the UK Singles Chart, a position it maintained for three weeks. Outside the United Kingdom, the single has topped the charts in Australia, New Zealand, Sweden and the Republic of Ireland. It also became his breakthrough hit in the US, peaking at number 11 on the Billboard Hot 100. Due to the longevity of the chart trajectory of the song, it peaked at number 11 on the Billboard Hot 100 year end charts.

Based on this passage, who wrote song say you wont let go?
To answer the question, consider the following: "Say You Wo n't Let Go" is a song by British singer and songwriter James Arthur.
So, the final answer is British singer and songwriter James Arthur.