Football fans who were at Liverpool’s Premier League title victory parade, where a car ploughed into pedestrians injuring more than 50 people, have said they were “staggered” by the traffic control measures in place before the incident.

A 53-year-old man from the West Derby area of the city was arrested on suspicion of attempted murder, driving while unfit through drugs, and dangerous driving. Merseyside police said detectives had been granted more time to question the man, with an extension until Thursday.

The force has identified 79 people who were injured in the incident on Water Street on Monday, with 50 treated in hospital. Of those, seven remained in hospital for treatment on Wednesday afternoon, all in a stable condition, police said.

“I’m pleased to say that the number of people in hospital is reducing as they continue to recover from the awful incident,” Det Supt Rachel Wilson said. “I want to reassure the public of Merseyside that detectives are making significant progress as we seek to establish the full circumstances that led to what happened.”

The police and Liverpool council have said that traffic management plans were in operation at the event, including rolling road closures and hostile vehicle measures.

The Merseyside police assistant chief constable Jenny Sims said on Tuesday: “We had worked extensively with event organisers and key partner agencies in the months ahead of the potential parade, and a robust traffic management plan was put in place, which included a number of local authority road closures throughout the route and the city centre.

“This included Water Street, which was closed to traffic. It is believed the driver of the Ford Galaxy car involved in the 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.”

​It is understood planning for this year’s parade began in February and was subject to rigorous testing which met national standards. ​The budget was​ also increased significantly ​from previous parades to enhance security, with​ costs met in full by Liverpool FC.

​“Hostile​ vehicle ​mitigation​” measures ​were in place along the 15km route. The plan included road closures and traffic diversions as well as road closure signage, traffic cones, accredited traffic stewards and ​traffic ​management ​vehicles, which were supported by police vehicles at key junctions.

As a final barrier, the measures included a 3.5 tonne HGV, used to prevent access from hostile vehicles to Water Street. This was an identified “red route” for emergency vehicle access.

However, many fans who attended the parade have said they had feared something could happen as “vehicles were edging and pushing through crowds” who had lined the streets to watch.

Paul Marsden, 57, a quality and risk manager from Flint, who had been watching the parade nearby, said: “I have to say, I wasn’t surprised. I saw time and again vehicles edging and pushing through crowds leading up to the parade and during it. I warned my sons to stay back because I could recall the Nice terror attack ploughing through crowds.”

He added: “I understand police and authorities want to keep parade access open for as much as possible but there needs to be lessons learned. When hundreds of thousands of people are close together, the traffic must be cordoned off with barriers protecting the whole route and not just the endpoints.”

Phil Williams, from Sunderland, who was watching the parade with his 15-year-old son Harry, said he had not seen “any traffic control measures to prevent him and other cars coming along there the way they did”.

“I’m absolutely staggered that the road closures didn’t go further,” he added.

Adrian Littlermore, 59, from Winchester, said that even outside the city centre, pedestrians were being “pushed into the road”.

He said: “You could tell the police there weren’t happy and were asking each other who was letting the cars through. There were probably 20 let through by the time we left and it was sectioned off so badly they were practically driving into the crowds.

“Police on the ground were doing their best, I don’t fault them at all, but it was clear it wasn’t under control. I’m not sure at one point, at the planning stage, if there was a breakdown in communication, but there were cars going where they weren’t supposed to be.

“There were people having to move their feet so the wheels didn’t go over them and people with buggies just having to stand in front of them to get between them and the cars. The drivers looked scared stiff as well, they didn’t want to be there. It wasn’t the fault of the police there, but it was like a free-for-all.”

On Wednesday the prime minister visited Merseyside police headquarters and met the deputy chief constable , assistant chief constable, the police and crime commissioner, Emily Spurrell, and the metro mayor, Steve Rotheram.

At the start of the meeting, Keir Starmer said: “Thank you all for making time. It’s really important for me to be here. The scenes on Monday were just awful, to see how incredible joy at an amazing achievement turned to horror in a moment.

“Steve, the mayor, has been keeping me informed and updated, along with my team, but it’s really important to be here to go through this first-hand with you, so thank you for making time and ensuring that I get to see the detail in the way that I’d like to.”

Rotheram said later that those who had assisted after the incident “encapsulated the true spirit” of the city.

“The response from so many to such a shocking incident has shown the very best of our region at a very difficult time,” he said.

“Scousers reacted, as I knew that they would, offering food and drink, warmth, somewhere to rest, even lifts across the country, and simple gestures like somewhere to charge phones or to help contact loved ones.

“As the injured recover and the city returns to normality, I hope that in time people will remember a spectacular parade of colour and joy.

“Thank you once again for those that assisted in whatever capacity and from wherever you come from, because you encapsulated the true spirit of this place that we’re so lucky to call home.”