When someone dies following police contact, it is mandatory for the case to be referred to the IOPC, which is now investigating.
The watchdog said on Saturday that “at this early stage, we understand Cleveland Police sighted a suspicious vehicle and a pursuit began.”
Security footage from a house on Lime Road in Middlesbrough appears to show a car being pursued by police vehicles three minutes before the crash.
The understands the pursuit ended prior to the crash, and the police vehicle occupied by PC Blades and PC Clough just happened to be in the area at the time.
IOPC Director of Investigations Nicola Marfleet called it a “tragic incident” and said her “thoughts are with family and friends and all those affected, including the emergency services in attendance.”
Shadow Home Secretary Chris Philp also shared his condolences, adding the IOPC “must be given the time and space to complete their investigations without speculation”.
The A66, which is the major artery through Teesside and the location of the crash is surrounded by industrial units and factories, remained closed on Sunday.