| O Pizza and Kebab Ltd | Hospitality | 2023 |
| O&A Catering Limited | Hospitality | 2025 |
| O&A Food Van Limited | Hospitality | 2024 |
| O&D Couriers Ltd | Transport & logistics | 2019 |
| O&H (Drapery) Limited | Real estate | 2018 |
| O&H (OBS 1) Limited | Real estate | 2018 |
| O&H (OBS 2) Limited | Real estate | 2018 |
| O&M Lets Ltd | Real estate | 2023 |
| O&Z Services Ltd | Construction | 2025 |
| O'Brien Swift Limited | Construction | 2022 |
| O'Lare Limited | Information & communication | 2022 |
| O'Neill Engineering Services Limited | Construction | 2018 |
| O.A.B Direct Ltd | Transport & logistics | 2021 |
| O.Richmond Ltd | Transport & logistics | 2025 |
| O.S (Cambs) Limited | Transport & logistics | 2026 |
| O.W.W.O Speedtrans Ltd | Transport & logistics | 2025 |
| OA Medicos Ltd | Health & social care | 2026 |
| OA Smiles Ltd | Health & social care | 2025 |
| OAB Lets Ltd | Real estate | 2023 |
| Oak Activities Ltd. | Arts & recreation | 2015 |
| Oak Barton Farm CIC | Agriculture & fishing | 2024 |
| Oak Court Business Park Limited | Real estate | 2020 |
| Oak Drive Peakirk Limited | Construction | 2025 |
| Oak House Homecare Cambs Ltd | Health & social care | 2016 |
| Oak House Homecare Ltd | Health & social care | 2000 |
| Oak Lettings Ltd | Households | 2020 |
| Oak Logistics Ltd | Transport & logistics | 2018 |
| Oak Serviced Accomodation Ltd | Hospitality | 2025 |
| Oak Tree Design & Build Limited | Construction | 2019 |
| Oak Tree Design & Build Services Limited | Construction | 2013 |
| Oaka LLP | | 2012 |
| Oaka Properties Limited | Real estate | 2023 |
| Oakdale VET Centre Limited | Professional & scientific | 2009 |
| Oakdene Hollins Ltd. | Professional & scientific | 1994 |
| Oakes Advisory Ltd | Information & communication | 2025 |
| Oakgrove Acres Limited | Real estate | 2022 |
| Oakham Ales Limited | Professional & scientific | 2004 |
| Oakham Heights Allotment Gardens Limited | Households | 2012 |
| Oakhouse Financial Holdings Ltd | Professional & scientific | 2018 |
| Oakhurst Group Ltd | Financial services | 2019 |
| Oakhurst Professional Services Ltd | Professional & scientific | 2021 |
| Oakhurst Property Investment Ltd | Real estate | 2018 |
| Oakley House Management Company Limited | Households | 2018 |
| Oakley Lodge Limited | Real estate | 2010 |
| Oakmont Care Ltd | Public administration | 2018 |
| Oakmont Installations Ltd | Construction | 2023 |
| Oakpolytech Ltd | Professional & scientific | 2023 |
| Oakridge Residential Management Company Limited | Households | 2006 |
| Oakshott Holdings Ltd | Financial services | 2025 |
| Oakstone Solutions Ltd | Information & communication | 2025 |
| Oaktree Court a RTM Limited | Real estate | 2025 |
| Oaktree Court B RTM Limited | Real estate | 2025 |
| Oakwave Trading Limited | Administrative & support | 1991 |
| Oakwood 303 Management Company Limited(The) | Households | 1982 |
| Oakwood Consultants 2015 Ltd | Professional & scientific | 2014 |
| Oakwood Financial Services 2015 Ltd | Professional & scientific | 2014 |
| Oakwood Motor Group Ltd | Wholesale & retail | 2025 |
| Oakwood Park (Moulton Seas END) Management Company Limited | Households | 2003 |
| Oakwood Property Management 2015 Ltd | Real estate | 2014 |
| Oakwood Property Portfolio Limited | Hospitality | 2017 |
| Oana 87 Ltd | Transport & logistics | 2024 |
| OB Therapies Ltd | Other services | 2022 |
| OBA Independent Trading Co CLG Ltd | Financial services | 2025 |
| Objective Cyber Ltd | Information & communication | 2020 |
| Observable Property Investment Limited | Real estate | 2021 |
| Obsession Dancewear Ltd | Wholesale & retail | 2024 |
| Obsidian Aviation Ltd | Professional & scientific | 2021 |
| Obsidian Noir Developments Limited | Construction | 2025 |
| OCC Automation Limited | Administrative & support | 2018 |
| OCC Polo Ltd | Other services | 2020 |
| Occupation Road Property Limited | Real estate | 2017 |
| Ocean Care Residence Marvel House Ltd | Public administration | 2026 |
| Ocean News Limited | Wholesale & retail | 2016 |
| Ocean Supported Living Ltd | Administrative & support | 2025 |
| Ocean United Limited | Construction | 2020 |
| Ocholaxpress Ltd | Transport & logistics | 2025 |
| OCI Gateway Ltd | Administrative & support | 2023 |
| Ocool Refrigeration Ltd | Manufacturing | 2024 |
| Ocs-Uk IT Ltd | Information & communication | 2011 |
| Octagon Developments (Cambs) Limited | Real estate | 2016 |
| Octane Car Sales Ltd | Wholesale & retail | 2024 |
| Octopus Consulting Solutions Limited | Professional & scientific | 2023 |
| Octopus Strategy Consultancy Ltd | Information & communication | 2024 |
| Oculus EYE Care Limited | Other services | 2016 |
| OD & B Electrical Services Limited | Construction | 2026 |
| OD IT Solutions Limited | Information & communication | 2025 |
| Odageru Trans Ltd | Administrative & support | 2017 |
| Odbros Ltd | Wholesale & retail | 2021 |
| Odedra Financial Solutions Ltd | Professional & scientific | 2014 |
| Odedra's Enterprise Limited | Wholesale & retail | 2023 |
| Oderson Brickwork Services Ltd | Construction | 2021 |
| Odessalux Ltd | Water & waste | 2023 |
| Odiz Newsagents Limited | Wholesale & retail | 2023 |
| Odling Development Ltd | Households | 2022 |
| OEE Investments Limited | Real estate | 2020 |
| OEL Electrical Ltd | Construction | 2011 |
| Offre ET Demande Agricole UK Limited | Administrative & support | 2009 |
| Ofili Ventures Limited | Administrative & support | 2022 |
| Ofoase Zongo Youth Diaspora ASS. UK Ltd | Other services | 2026 |
| Ofosu Services Limited | Health & social care | 2017 |