| Nvoyy Group Ltd | Information & communication | 2015 |
| Nwcp Ltd | Professional & scientific | 2024 |
| Nwpmotors Ltd | Wholesale & retail | 2025 |
| NXT Steps Recruitment Ltd | Administrative & support | 2019 |
| Nyala Properties Limited | Real estate | 2024 |
| Nyara Ventures Ltd | Transport & logistics | 2024 |
| Nygate Group Ltd | Information & communication | 2020 |
| Nyim Publishing Ltd | Information & communication | 2020 |
| Nyin Limited | Professional & scientific | 2024 |
| Nyquist Limited | Wholesale & retail | 2021 |
| O & B Enterprises Ltd | Hospitality | 2013 |
| O & R Property (Suffolk) Limited | Real estate | 2025 |
| O and T Solutions Ltd | Other services | 2024 |
| O George Properties Ltd | Real estate | 2025 |
| O J Neil Biomass Limited | Agriculture & fishing | 2016 |
| O Litoral Ltd | Administrative & support | 2023 |
| O Murchu Ltd | Real estate | 2021 |
| O&L I. Specialist Legal Ltd | Professional & scientific | 2023 |
| O&L Specialist Ltd | Professional & scientific | 2025 |
| O' Care Services Ltd | Administrative & support | 2018 |
| O'Dwyer Properties Ltd | Real estate | 2024 |
| O. Seaman & SON Limited | Construction | 1975 |
| O.Atoba Ltd | Real estate | 2026 |
| O.C. Jewers & Sons Limited | Real estate | 2013 |
| O.K Fencing Limited | Administrative & support | 2003 |
| O.Piscikas Ltd | Transport & logistics | 2025 |
| O.S.A.T Ltd | Education | 2011 |
| Oak Group Estates Ltd | Real estate | 2026 |
| Oak View Living Limited | Real estate | 2025 |
| Oakdale Freeholders Management Limited | Households | 1998 |
| Oakes Barn Ltd | Real estate | 2010 |
| Oakhay Court Residents Co Ltd | Households | 2019 |
| Oakland Car Sales Ltd | Wholesale & retail | 2025 |
| Oaklands Developments (Anglia) Limited | Construction | 2006 |
| Oakley Civil Engineering Limited | Construction | 2013 |
| Oakmere Estates Limited | Real estate | 2021 |
| Oakpark Properties (East Anglia) Limited | Real estate | 2000 |
| Oaks Drive Management Limited | Real estate | 1999 |
| Oaks Management Services Limited | Households | 2020 |
| Oaks Office Park Management Company Limited | Real estate | 2005 |
| Oaks Pizza Limited | Hospitality | 2018 |
| Oaktree Associated Holdings Limited | Financial services | 2014 |
| Oaktree UK Limited | Wholesale & retail | 2001 |
| Oakwells Asset Management Limited | Construction | 2026 |
| Oakwells Beccles Limited | Construction | 2025 |
| Oakwood Park (Stowmarket) Management Company Limited | Households | 2007 |
| Oarsman Software Ltd | Information & communication | 2025 |
| Oasi Root Plant-Based Ltd | Hospitality | 2025 |
| Oasis Heritage Properties Ltd | Construction | 2025 |
| OAT Home Limited | Wholesale & retail | 2024 |
| Oben Nutrition UK Ltd | Wholesale & retail | 2025 |
| Oberon Traders Ltd | Wholesale & retail | 2026 |
| Obique Ltd | Manufacturing | 2013 |
| Objectivity Training UK Ltd | Information & communication | 2016 |
| Oblex Digital Limited | Information & communication | 2024 |
| Oblivious Studios Limited | Information & communication | 2021 |
| Obolex Ltd | Professional & scientific | 2025 |
| Obsessed by Stephanie OGU Limited | Wholesale & retail | 2023 |
| Obsidia Ltd | Financial services | 2020 |
| Obsidian Contracts Ltd | Energy | 2024 |
| Obsidian Moon Ltd | Arts & recreation | 2025 |
| Obsidian Partners Limited | Financial services | 2019 |
| Obsidian State Ltd | Professional & scientific | 2025 |
| Ocavic Services Limited | Professional & scientific | 2023 |
| Occubly Ltd | Information & communication | 2020 |
| Ocealune Ltd | Wholesale & retail | 2025 |
| Ocean Analytics Ltd | Professional & scientific | 2025 |
| Ocean ASH Ltd | Information & communication | 2025 |
| Ocean City Automotive Ltd | Wholesale & retail | 2025 |
| Ocean City Prizes Ltd | Arts & recreation | 2025 |
| Ocean Soul Co. Ltd | Wholesale & retail | 2026 |
| Oceana Developments Limited | Construction | 2025 |
| Oceana Group Holdings Limited | Financial services | 2025 |
| Oceanic Leads Limited | Real estate | 2025 |
| Oceanlink Logistics Ltd | Transport & logistics | 2025 |
| Oceanus Group Ltd | Information & communication | 2020 |
| Oceanus Management Services Limited | Wholesale & retail | 2023 |
| OCR Consulting Ltd | Professional & scientific | 2008 |
| Octacorp Holdings International Limited | Wholesale & retail | 2025 |
| Octantis Fabrication Limited | Wholesale & retail | 2024 |
| Octimedia Limited | Administrative & support | 2023 |
| Oculus Wealth Management (Bury ST Edmunds) Limited | Financial services | 2014 |
| OCZ Ltd | Wholesale & retail | 2022 |
| ODB Family Limited | Wholesale & retail | 2016 |
| ODD Socks International Ltd | Professional & scientific | 2019 |
| Odexp Innovations Ltd | Wholesale & retail | 2025 |
| ODH Mortgage Specialists Ltd | Financial services | 2026 |
| Odin Logistics Ltd | Transport & logistics | 2025 |
| Odingames Ltd | Information & communication | 2025 |
| Odity Holdings Limited | Wholesale & retail | 2024 |
| ODL Ltd | Wholesale & retail | 2015 |
| Odriscproperty Ltd | Real estate | 2025 |
| Oduro Pharmaceuticals Ltd | Agriculture & fishing | 2019 |
| Odus Consultancy Limited | Information & communication | 2022 |
| Odyssey Walk in Baths Ltd | Wholesale & retail | 2022 |
| OFF World Events Limited | Information & communication | 2026 |
| Officially Signed Ltd | Wholesale & retail | 2017 |
| Offlyn Ltd | Wholesale & retail | 2026 |
| OG Brands Ltd | Wholesale & retail | 2024 |
| OG Wear Ltd | Wholesale & retail | 2025 |