| Ocular Melanoma UK | Health & social care | 2012 |
| Odeyssa Avenue Ltd | Wholesale & retail | 2025 |
| Odogwu Limited | Professional & scientific | 2016 |
| Odyssey Oasis Ltd | Administrative & support | 2025 |
| Off-Road Activity Centre CIC | Education | 2018 |
| Office for Architectural Culture Limited | Professional & scientific | 2011 |
| Office X Ltd | Wholesale & retail | 2016 |
| Offshore HV & Fibre Ltd | Professional & scientific | 2014 |
| Oforaziri Limited | Arts & recreation | 2018 |
| OG Vapes Limited | Other services | 2018 |
| Ogvalley Marketing Ltd | Wholesale & retail | 2023 |
| Ohanaa Ltd. | Construction | 2016 |
| OHM Electrical Consultancy Limited | Other services | 2014 |
| OI Visas Ltd | Administrative & support | 2022 |
| Oiikii Jobs Limited | Administrative & support | 2023 |
| Oiikii Limited | Information & communication | 2021 |
| Oiyaa Group Limited | Administrative & support | 2025 |
| Oiyaa Technologies Limited | Administrative & support | 1999 |
| Ojas Consulting Limited | Information & communication | 2011 |
| OK Property Ltd | Real estate | 2024 |
| Okanlawon Ltd | Administrative & support | 2019 |
| Okoluv Ltd | Wholesale & retail | 2026 |
| OL Sorts Ltd | Wholesale & retail | 2017 |
| OLA Davies Ltd | Health & social care | 2023 |
| Old Garden Ltd | Hospitality | 2018 |
| Old Pound Estates Ltd | Real estate | 2017 |
| Oldham 243 Ltd | Construction | 2025 |
| Oldie Buddy Ltd | Administrative & support | 2021 |
| Olek Ltd | Construction | 2026 |
| OLESEN87 Ltd | Construction | 2026 |
| OLI Spencer Photography Limited | Professional & scientific | 2022 |
| Olimpio Class Transfers Limited | Transport & logistics | 2014 |
| Olineuk Ltd | Education | 2024 |
| Olive Branch Collection Ltd | Construction | 2025 |
| Olive Leaf Clothing Limited | Wholesale & retail | 2021 |
| Olive Rehana Ltd | Wholesale & retail | 2026 |
| Olive Sports Ltd | Transport & logistics | 2025 |
| Olive Tree Digital Limited | Information & communication | 2023 |
| Oliver Offset Limited | Manufacturing | 2017 |
| Olivia Transport Ltd | Transport & logistics | 2020 |
| Ologia Ltd | Administrative & support | 2017 |
| Olsenport Limited | | 1981 |
| Oludeniz Ltd | Wholesale & retail | 2016 |
| OLW Top Ware Limited | Wholesale & retail | 2025 |
| Olympia Removals Ltd | Transport & logistics | 2021 |
| Olympia Star Holdings Limited | Financial services | 2022 |
| Olympus 1 Drinks Limited | Wholesale & retail | 2025 |
| OM Global Ltd | Wholesale & retail | 2025 |
| OM Residential Limited | Real estate | 2025 |
| OM SAI Transport Limited | Transport & logistics | 2021 |
| Oman Traders Ltd | Real estate | 2026 |
| Omani Jewellery Ltd | Wholesale & retail | 2026 |
| Omar Designs SQ Limited | Construction | 2024 |
| Omart Creations Ltd | Information & communication | 2022 |
| Omasatis Limited | Real estate | 2021 |
| Omay Global Ltd | Information & communication | 2023 |
| Omay Properties Ltd | Real estate | 2024 |
| Omega 21 Ltd | Real estate | 2025 |
| Omega Engineers Ltd | Information & communication | 2011 |
| Omega GROUP0 Ltd | Construction | 2012 |
| Omega Worldwide Logistics Solutions Ltd | Transport & logistics | 2021 |
| Omezi Ltd | Manufacturing | 2024 |
| OMI Transport Ltd | Transport & logistics | 2022 |
| Omisha Limited | Construction | 2023 |
| Omnio Ventures Ltd | Professional & scientific | 2025 |
| ON Call Pharma UK Ltd | Other services | 2017 |
| ON Move Ltd | Wholesale & retail | 2021 |
| ON SET Tech Ltd | Information & communication | 2013 |
| ON Site Car Wash Limited | Administrative & support | 2025 |
| ON Target Posh Limited | Administrative & support | 2020 |
| ON the Green Enterprises Limited | Financial services | 2022 |
| ON the Spot Car Wash Limited | Administrative & support | 2023 |
| ON the Tiles (Hillingdon) Ltd | Construction | 1999 |
| ON the Wheelz Limited | Transport & logistics | 2016 |
| ON Top Roof & Build Ltd | Construction | 2025 |
| ON Trac Roofing Services Limited | Construction | 2025 |
| ON Trac Services Limited | Transport & logistics | 2025 |
| On-Site Medical Services Limited | Education | 2017 |
| Onbord Ltd | Transport & logistics | 2016 |
| Oncas Ltd | Health & social care | 2021 |
| One Business Solutions Ltd | Professional & scientific | 2021 |
| One Call Transport Limited | Transport & logistics | 2022 |
| One Cargo and Courier Ltd | Transport & logistics | 2018 |
| One Life Health Support B Ltd | Administrative & support | 2025 |
| One Life Holding Ltd | Financial services | 2025 |
| One Orchard House Limited | Real estate | 2021 |
| One Path Requirement Ltd | Administrative & support | 2024 |
| One Smile Healthcare Ltd | Health & social care | 2022 |
| One Some Ltd | Other services | 2018 |
| One Step Above Limited | Other services | 2017 |
| One Stop Couriers Limited | Transport & logistics | 2000 |
| One Stop Hospitality Services Ltd | Construction | 2026 |
| One Stop Logistics Limited | Transport & logistics | 2013 |
| One Stop Recovery 24/7 Ltd | Wholesale & retail | 2019 |
| One TEN Travel Ltd | Transport & logistics | 2026 |
| One World Travel Services Limited | Transport & logistics | 2021 |
| Onebikecustoms Ltd | Wholesale & retail | 2025 |
| Onebsh Limited | Financial services | 2020 |
| Onebuild Developments Group Ltd | Construction | 2026 |
| Oneffl Limited | Real estate | 2017 |