| Nzed Projectco 6 Limited | Energy | 2026 |
| Nzed Projectco 7 Limited | Energy | 2026 |
| Nzed Projectco 8 Limited | Energy | 2026 |
| Nzed Projectco 9 Limited | Energy | 2026 |
| O'Connell Property Development Limited | Construction | 2024 |
| Oak & Stone Renovations Limited | Construction | 2021 |
| Oakbridge Property Ventures Ltd | Real estate | 2026 |
| Oakdene Nursery Limited | Education | 2003 |
| Oaken Gates Limited | Professional & scientific | 1972 |
| Oakland Surveys Ltd | Professional & scientific | 2024 |
| Oakleaf Property Maintenance Ltd | Administrative & support | 2022 |
| Oakley and Irvine Stratford Upon Avon Limited | Other services | 2014 |
| Oakley Blythe Quantity Surveyors Ltd | Professional & scientific | 2018 |
| Oakley Wood Developments (Leamington) Limited | Financial services | 2019 |
| Oakley Wood Developments (Leamington) Phase 2 Limited | Construction | 2022 |
| Oakley Wood Fitters Ltd | Manufacturing | 2025 |
| Oakley Wood Joinery Ltd | Manufacturing | 2024 |
| Oakrose Estates Limited | Construction | 2024 |
| Oakville Events Ltd | Other services | 2017 |
| OAS Global Ltd | Information & communication | 2026 |
| Oberoi Group of Companies Limited | Hospitality | 2018 |
| Oberoi Group UK Ltd | Professional & scientific | 2020 |
| Oberoi Hotels Limited | Hospitality | 2018 |
| Oberoi Travels & Tourism UK Ltd | Administrative & support | 2017 |
| Obford Ltd | Information & communication | 2026 |
| OC Security Consultancy Ltd | Administrative & support | 2019 |
| Ocean Gold Vitality Ltd | Extraterritorial | 2024 |
| OCO Management Limited | Professional & scientific | 2017 |
| OD Logistics Ltd | Transport & logistics | 2026 |
| Odehomes Ltd | Real estate | 2023 |
| OEC Airport Transfers Ltd | Transport & logistics | 2023 |
| OFF Street Parking Limited | Administrative & support | 2020 |
| Offchurch Bury Polo Club (Holdings) Limited | Agriculture & fishing | 2018 |
| Offchurch Bury Polo Club Limited | Agriculture & fishing | 2018 |
| Office Mango Ltd | Information & communication | 2024 |
| Office Supplies Depot Limited | Wholesale & retail | 2021 |
| Official Security Ltd | Administrative & support | 2025 |
| Offpro Ltd | Extraterritorial | 2007 |
| OGC Group Limited | Manufacturing | 2022 |
| Ogilvie Services Limited | Construction | 2015 |
| OH My! Studio Limited | Information & communication | 2014 |
| OHL Consulting(Uk) Ltd | Professional & scientific | 2023 |
| Oishini Analytics Ltd | Information & communication | 2024 |
| OJ Nibl Limited | Professional & scientific | 2022 |
| OJT Commercial Ltd | Administrative & support | 2026 |
| OJT Designs Limited | Administrative & support | 2011 |
| OK2UK Ltd | Education | 2008 |
| Okobase Ltd | Wholesale & retail | 2020 |
| Okobnb Ltd | Real estate | 2024 |
| Okogroupe Ltd | Wholesale & retail | 2019 |
| Okopod Ltd | Manufacturing | 2019 |
| Olan Property Consultancy Limited | Professional & scientific | 2020 |
| Old Beginnings Ltd | Arts & recreation | 2025 |
| Old Hall Consulting Limited | Professional & scientific | 2010 |
| Old Lodge Estate Rental Property Limited | Real estate | 2019 |
| Old Lodge Estates 2 Limited | Real estate | 2017 |
| Old Lodge Estates 3 Ltd | Real estate | 2019 |
| Old Lodge Estates Limited | Real estate | 2017 |
| Old School of Driving Ltd | Education | 2024 |
| Old Town Restorations Ltd | Wholesale & retail | 2020 |
| Old Warwickian Trust | Education | 2011 |
| Older & Wiser Ltd | Transport & logistics | 2020 |
| Oldfield and LEE Limited | Professional & scientific | 2023 |
| Oleht Holdings Limited | Real estate | 2023 |
| Olive and Barr Ltd | Manufacturing | 2018 |
| Oliver Jacob Consulting Limited | Professional & scientific | 2012 |
| Olivers Fitted Furniture Pershore Limited | Wholesale & retail | 2019 |
| Olivers Shipston Limited | Wholesale & retail | 2019 |
| Olivia Knight Property Limited | Households | 2019 |
| OM Acquisition Trading Ltd | Real estate | 2023 |
| Omer Smile Ltd | Health & social care | 2017 |
| Omishka Ltd | Wholesale & retail | 2022 |
| Omishka Online Ltd | Wholesale & retail | 2022 |
| Omishka Shop Limited | Wholesale & retail | 2023 |
| Omni Grid Energy Limited | Manufacturing | 2025 |
| Omnitel Consulting Limited | Information & communication | 2012 |
| Omnivest Ltd | Extraterritorial | 2025 |
| Omonia Consulting Ltd | Professional & scientific | 2025 |
| Omore (UK) Limited | Hospitality | 2014 |
| ON Demand Services Ltd | Transport & logistics | 2023 |
| ON Point Cars Ltd | Wholesale & retail | 2022 |
| ON the Mark Copy & Concepts Limited | Professional & scientific | 2015 |
| ON the Rocks Bar & Restaurants Ltd | Hospitality | 2016 |
| ON Track Law Ltd | Professional & scientific | 2022 |
| One Extreme Limited | Information & communication | 2006 |
| One Hospitality Management Limited | Hospitality | 2023 |
| One Second Ltd | Professional & scientific | 2014 |
| One Stop Cleaning (UK) Limited | Other services | 2013 |
| One Stop Cleaning Kenilworth Limited | Other services | 2014 |
| Onebazaar Ltd | Wholesale & retail | 2024 |
| Oneday Property Limited | Real estate | 2016 |
| Online Energy Referral Services Limited | Information & communication | 2025 |
| Ontrack Compliance Ltd | Professional & scientific | 2023 |
| Oo&T Limited | Wholesale & retail | 2020 |
| Opeia Investment Limited | Real estate | 2025 |
| Opeia Property Limited | Real estate | 2024 |
| Open ALL Hours (Leamington) Limited | Wholesale & retail | 2008 |
| Open Aqua Ltd | Wholesale & retail | 2022 |
| Open Closed Software Ltd | Information & communication | 2022 |
| Opening Minds Montessori School Ltd | Education | 2025 |