RAF Westland "Sea King" in the bright yellow SAR livery.

Used to see these practising "on exercise" or working with the RNLI or Mountain Rescue in many places around the UK - along Hadrian's Wall, the Lake District or North Wales in particular.
Loverly & distinctive sound. Seeing this brought back some nice memories of various "Lifeboat / Harbour Days"

en.wikipedia.org/wiki/Westland_Sea_King