As it stands 14 people in total have been arrested in connection with the investigation, of which two people have since been released without charge.
A screengrab of the Manchester Arena following a bomb blast during a concert at the venue.
Great Manchester Police said a 23-year-old man was arrested Monday in Shoreham-by-Sea on suspicion of terrorism offenses.
Members of the Manchester suicide bomber's network are still potentially at large, British interior minister Amber Rudd said on Sunday, after the terrorism threat level was lowered due to significant progress in the investigation.
When asked how many potential militants the government was anxious about, Rudd said the security services were looking at 500 potential plots, involving 3,000 people as a "top list", with a further 20,000 below that.
Thousands of people took to the streets for the Great Manchester Run as the latest large-scale event took place in the city in the wake of the terror attack.
Police have identified the attacker as 22-year-old Salman Abedi, a Manchester native, and are working to piece together his movements in the final weeks before the bombing as well as who else may have been involved.
As the huge counter-terror operation continued, the NHS said 54 people injured in the attack were still being treated in eight hospitals with 19 receiving critical care.
The photos show a nondescript Salman Abedi, with glasses and a black baseball cap, dressed in jeans and a dark jacket, in the last minutes before the murder of 22 people.
Abedi's brother and father also were arrested in Libya last week where they are being held.
There was a visible police presence as runners gathered on the start line for the Manchester run on Sunday morning.
Police officers from Wales were among those helping out as a heightened security operation remained in place.
MI5 are looking at decisions taken in the case of Abedi, who used to be on a terror watch list but was no longer on it at the time of the attack, and whether warnings about his behaviour were ignored amid mounting criticism of the security services.
The family of Georgina Bethany Callander, an 18-year-old killed in the bombing, released a tribute on Saturday in which they called on the government to "open its eyes" to prevent further tragedy.