The auctioneers in the fish market scene are real fish auctioneers from North Shields fish quay (where the scene was filmed). The others in that scene are, however, extras.
The scenes with the finding of the Stonnel van with links to Quinn, the fire on the boat, and some of the "beach hut" scenes, all in an area referred to as Blythe Point, were all filmed at the mouth of the River Tees. The final scenes where the murderer confesses were also filmed here.
Phillip Hill-Pearson and Ciaran Griffiths also starred in The Bay which centred around fishing trawlers and a murder mystery
The green fisherman huts can be found at South Gate, Redcar, Yorkshire, quite a few miles from Northumberland.