Police have been criticised for not revealing more information about a “mysterious” material that sparked an 11-hour closure of the M3.
Thousands of motorists were caught up in long queues when it was shut on Saturday between junctions nine and 11.
Former Hampshire Police and Crime Commissioner (PCC) Simon Hayes told the BBC: “The public deserve to be told and understand what happened.”
The substance was flammable but not explosive, police have said.
Mr Hayes said communication from the police’s public relations department was “a disaster”.
He added: “I would hope there is a jolly good reason for it [the motorway] to be closed. There’s been nothing from the office of the PCC and the whole thing is really very mysterious.”
The discovery of the substance, thrown from a bridge, saw military bomb disposal experts called to the scene near Winchester.
The motorway was closed shortly before 04:00 BST and fully reopened by about 15:30.
Police said tests were being carried out to determine what the substance was.
The force said nobody was hurt and there was no wider risk to public safety. It also confirmed it was not being treated as a terrorist incident.
The BBC has requested fuller details from the force, but it has yet to respond. Current PCC Michael Lane has also been asked to comment.