The phenomenon is caused by a regular rainbow and a sunset happening at the same time.
Rainbow - Wikipedia
Rare rainbow-coloured nacreous clouds seen across Yorkshire - BBC News
Unusual 'rainbow' clouds spotted in the south east - BBC Weather
Rainbow clouds spotted in the East for first time since 2016 - BBC
Spectacular red rainbow illuminates historic English town – but
Beautiful Pink Rainbows Light Up Sky Over England
Pink rainbows spotted over south and west of England
Cause of 'Stranger Things' pink lights over Yorkshire town
In Pictures: Rainbow clouds captured on camera in the south
White rainbow spotted close to M5 motorway near Bristol - BBC News
Pink rainbows spotted over south and west of England - BBC News
Rare 'pink rainbow' spotted in sky over Bristol
Pink rainbows spotted over south and west of England - BBC News
White rainbow spotted close to M5 motorway near Bristol - BBC News