Hampshire Police say yesterday's incident which closed the M3 for 11 hours was NOT a terrorist incident.
But they have confirmed they were called to the motorway, between Junctions 9 and 11, at 3.40am on Saturday, following reports hazardous material had been spotted on the carriageway.
The force said it was only right that a full investigation was carried out, though they recognised the closure caused significant disruption and inconvenience for motorists:
Both the motorway and surrounding roads were gridlocked for most of the day, with some people concerned about the lack of information.
Others praised emergency services for handing out bottled water and called for others to make the best of a bad situation.
Police also revealed they were ivestigating a similar incident which took place on the same bridge last week, at around 4am on Saturday 16th September.