Local Merseyside Police are now stating a Ford Galaxy avoided a roadblock at the parade by tailgating an ambulance responding to reports of a heart attack amongst the celebrating crowd at the parade.
Police say the 53 year-old man is from Liverpool's West Derby area and was also being detained on suspicion of dangerous driving and driving while unfit through drugs.
The incident occurred shortly after 6pm on Monday leaving 50 people needing hospital treatment. Of the injured, police say, 11 remained in hospital. All are said to be in a "stable" condition.
Police statement
Merseyside's Assistant Chief Constable Jenny Sims said: "It is believed the driver of the Ford Galaxy car involved in this incident was able to follow an ambulance on to Water Street, after the roadblock was temporarily lifted so that the ambulance crew could attend to a member of the public who was having a suspected heart attack."
Sims added: "There was no intelligence to suggest an incident of this nature would take place and, as we previously stated, the incident is not being treated as terrorism."