What are the best British detective TV series?

Foyle's War is a period drama TV show commissioned by ITV . Foyle's War was first aired in 2002 and ended after eight seasons. It features Michael Kitchen, Honeysuckle Weeks, Anthony Howellin the lead cast.

Prime Suspect revolves around the investigation of the first female police detective in London about a series of serial killings. She is determined to rise through the ranks of a chauvinistic police force. 

The Fall is a British-Irish crime thriller television series created by Allan Cubitt starring Gillian Anderson and Jamie Dornan that aired on BBC Two and RTE One from 2013 to 2016 with three seasons.

River is a six-episode British television crime-drama series written and created by Abi Morgan starring Stellan Skarsgard and Nicola Walker. It first premiered on BBC One in October 2015 then on Netflix in November 2015. 

Broadchurch is an English television crime drama broadcast on ITV which was written and created by Chris Chibnall. It only lasted until season three which last aired on April 17, 2017.