The data includes high street, hospitality and office workers based the town centre.
However, an expert at the think-tank said they were unable to differentiate between the sectors that workers returning to the city centre were employed in.
Paul Clement, chief executive of Ipswich Central business improvement district, said the Centre for Cities study was "incredibly surprising" and "incredibly disturbing".
Paul Clement, chief executive of Ipswich Central
- Credit: Archant
"Certainly most of the offices that are part of the business improvement district (BID) are beginning now to return people to their desks, albeit on a sort of part time hybrid basis.