| Commissionaire Garage Doors Limited | Manufacturing | 2009 |
| Common Ground Theatre Company Limited | Arts & recreation | 2007 |
| Commonsense Services (Norfolk) Limited | Administrative & support | 2014 |
| Commsquare Limited | Information & communication | 2007 |
| Communicate & Care Ltd. | Health & social care | 2012 |
| Community 4'RCE Community Interest Company | Education | 2011 |
| Community Action Suffolk | Health & social care | 2012 |
| Community Hub Ipswich CIC | Other services | 2020 |
| Community POP Chorus CIC | Arts & recreation | 2023 |
| Community Support Network C.I.C. | Hospitality | 2024 |
| Compair Crescent Ltd | Real estate | 2022 |
| Compair Media Limited | Administrative & support | 2023 |
| Compair Properties Ltd | Administrative & support | 2023 |
| Companion Cabbie Ipswich Ltd | Health & social care | 2017 |
| Compass Heating Installations Limited | Manufacturing | 2001 |
| Compass-Ai Technology Limited | Information & communication | 2024 |
| Compex Electrical Services Limited | Construction | 2022 |
| Complete Casting Services Ipswich Ltd | Wholesale & retail | 2008 |
| Complete Construction & Development Limited | Construction | 2008 |
| Complete Vehicle Solutions (UK) Limited | Administrative & support | 2011 |
| Completely Canine Ltd | Administrative & support | 2023 |
| Completion Property Group Ltd | Real estate | 2019 |
| Complex Case Management and Clinical Consultancy Ltd | Health & social care | 2024 |
| Complex Numbers Limited | Information & communication | 2002 |
| Complexus Spinal Care Limited | Health & social care | 2022 |
| Compliant Telecom Ltd | Information & communication | 2026 |
| Complynet Limited | Administrative & support | 2021 |
| Comprehensive Ltd | Other services | 2018 |
| Compton Property Investment Limited | Real estate | 2021 |
| Computer GP Limited | Information & communication | 2006 |
| CON Maintenance Limited | Administrative & support | 2025 |
| CON Spedition Ltd | Transport & logistics | 2025 |
| Conatus Bookkeeping Limited | Professional & scientific | 2015 |
| Conatus Financing Solutions Limited | Professional & scientific | 2011 |
| Conatus Holdings Limited | Financial services | 2020 |
| Concept Design Services (U.K.) Limited | Construction | 1986 |
| Concept Flooring Solutions Ltd | Construction | 2016 |
| Concertus Derbyshire Limited | Construction | 2019 |
| Concertus Derbyshire Traded Limited | Construction | 2021 |
| Concertus Design and Property Consultants Limited | Construction | 2013 |
| Concertus Suffolk Limited | Construction | 2013 |
| Concorde Care in the Community Limited | Professional & scientific | 2019 |
| Conect&Go Ltd | Wholesale & retail | 2021 |
| Confabricor Ltd | Professional & scientific | 2012 |
| Confidence Estates Limited | Real estate | 2021 |
| Confident Hire Limited | Administrative & support | 2025 |
| Conga Limited | Manufacturing | 2015 |
| Coniston Court (Putney) Limited | Households | 1982 |
| Conjor Investment Limited | Health & social care | 2019 |
| Connect Highways Ltd | Administrative & support | 2024 |
| Connect Highways Projects Ltd | Administrative & support | 2025 |
| Connect Highways Traffic Management Limited | Administrative & support | 2021 |
| Connect Maths Tutoring Ltd | Education | 2025 |
| Connecting the Dots Solutions Limited | Professional & scientific | 2025 |
| CONNECTINGA2B Ltd Ltd | Professional & scientific | 2024 |
| Connectionsphere Ltd | Information & communication | 2025 |
| Connells Kitchens and Bathrooms and Kitchens Ltd | Other services | 2023 |
| Conor Styles Carpentry Limited | Construction | 2021 |
| Conponi Group Ltd | Professional & scientific | 2023 |
| Conscious Capital Holdings Limited | Professional & scientific | 2024 |
| Consensum Limited | Professional & scientific | 2011 |
| Consensus Guillotine Engineering Limited | Manufacturing | 2002 |
| Consequentially Limited | Information & communication | 2012 |
| Conservative Environment Network | Administrative & support | 2013 |
| Consign Status Ltd | Wholesale & retail | 2025 |
| Consortium Consulting International Limited | Professional & scientific | 2024 |
| Conspicuous Interiors Ltd | Construction | 2018 |
| Constable Developments (Anglia) Limited | Real estate | 1977 |
| Constable Property Management Limited | Professional & scientific | 1994 |
| Constac Holdings Limited | Administrative & support | 2016 |
| Constance & Denny Ltd | Wholesale & retail | 2026 |
| Constantin D&C Ltd | Transport & logistics | 2023 |
| Constantine & Company (Exports) Limited | Transport & logistics | 1973 |
| Constantine Mechanical Services Ltd | Construction | 2019 |
| Constanza Chorus Limited | Education | 2016 |
| Construction Anglia Limited | Professional & scientific | 2024 |
| Construction Mechanical Engineering Ltd | Construction | 2015 |
| Construction Performance Solutions Limited | Professional & scientific | 2006 |
| Construction Recruitment Services Limited | Administrative & support | 2022 |
| Consulquest Limited | Professional & scientific | 2007 |
| Consult 818 Limited | Construction | 2017 |
| Consulting Direct Ipswich Limited | Professional & scientific | 2015 |
| Consulting for Access Limited | Information & communication | 2016 |
| Contador Accountancy Services Limited | Professional & scientific | 2018 |
| Contain-It Self Storage Limited | Transport & logistics | 2006 |
| Container Forwarding Solutions Ltd | Transport & logistics | 2019 |
| Containers and More Limited | Administrative & support | 2008 |
| Contempoary Enterprise Limited | Health & social care | 2017 |
| Contento PR Ltd | Professional & scientific | 2017 |
| Continental Tobacco UK Limited | Wholesale & retail | 2025 |
| Contisped Limited | Professional & scientific | 1976 |
| Contrast Cleaning Services (Suffolk) Ltd | Administrative & support | 2013 |
| Control Solutions Pest Control Ltd | Agriculture & fishing | 2018 |
| Control Trading Limited | Extraterritorial | 2007 |
| Convene Hospitality Ltd | Extraterritorial | 2025 |
| COO Ltd | Transport & logistics | 2018 |
| Cook Creative Media Ltd | Information & communication | 2019 |
| Cook Italian Limited | Wholesale & retail | 2010 |
| Cookie Barista Ltd | Hospitality | 2021 |
| Cool BEAN26 Limited | Hospitality | 2026 |