Three men - including one from Chesterfield - who are suspected of terrorism offences are entering a second week of questioning by detectives.
A week today, officers descended on Sheffield Road and arrested a 31-year-old man who has been identified as Hazhar Star in the national media.
Also known as Andy, he is understood to be the owner of the Mermaid Traditional Fish Bar on Sheffield Road.
Police also arrested two other men, aged 22 and 36, from Burngreave in Sheffield last Tuesday.
The arrests were made as part of an investigation by Counter Terrorism Policing North East (CTPNE).
All three men - who are being quizzed at a police station in West Yorkshire - are suspected of being concerned in the commission, preparation or instigation of acts of terrorism.
At this stage, there is no official word on what type of attack the suspects may have been planning - or when or where they might have carried it out.
A court has approved an extension giving counter-terrorism police until New Year’s Day - Monday - to hold and question the men.
A fourth man, a 41-year-old from Meersbrook in Sheffield, was arrested as part of the investigation but was released without charge.
A CTPNE spokesman said: “Extensive enquiries have satisfied the investigation that there are no grounds to charge him with any offences.
"We would like to reassure the public that public safety remains our priority at all times.”
On Friday, the army bomb disposal team carried out a controlled explosion to safely dispose of material found during thorough searches of the Mermaid Traditional Fish Bar building.
Those searches are now complete.
Councillor Barry Lewis, leader of Derbyshire County Council, said: "Police have done a remarkable job of protecting the public and preventing what could have been a terrible terrorist attack."
Chesterfield MP Toby Perkins described the controlled explosion as a 'further worrying development' and said: "Thanks to the police, security services and army who work so diligently and bravely to keep us protected."
Coun Tricia Gilby, leader of Chesterfield Borough Council, added: "I'd like to thank the residents who were evacuated from their homes and business owners who weren't able to open for their patience.
"We have every confidence in the police investigation."
The UK's terror threat level remains at 'severe', the second highest level.
Derbyshire police are urging people to continue to be vigilant but go about their business as usual.
As announced at the start of the month, armed police are patrolling the streets of Derbyshire over Christmas and New Year to make people feel safer.
Superintendent Michelle Shooter, of Derbyshire Constabulary, said: "I would like to thank the people of Chesterfield for their patience and understanding during the unavoidable disruption.
"Our officers have been working hard in support of CTPNE since the arrests were made on Tuesday and for that they also have my sincere thanks.
"We will continue patrolling the area to offer reassurance to the public.
"We'd ask that people remain calm, resilient and measured in what they say and how they act during the aftermath of what has been a difficult and concerning time for local communities."
If you see or hear something which could be terrorist related, act on your instincts and call the police in confidence on 0800 789 321.
In an emergency, always dial 999.
Visit act.campaign.gov.uk for more information.