| Oakhurst Woking Limited | Households | 2004 |
| Oakimage Limited | Real estate | 1994 |
| Oakland Developments Limited | Construction | 2011 |
| Oaklands 108 Properties Limited | Real estate | 2020 |
| Oaklands Court (Beckenham) RTM Company Limited | Households | 2016 |
| Oaklands Limited | Wholesale & retail | 1988 |
| Oaklands Prime Estates Limited | Real estate | 2025 |
| Oaklands Residents Management Association Ltd | Households | 2003 |
| Oaklawn Management Company Limited | Households | 2010 |
| Oakley Road Freehold Limited | Households | 2024 |
| Oakmead Christchurch Residents Association Limited | Households | 1999 |
| Oakmount House (Croydon) Management Company Limited | Households | 2022 |
| Oakridge (Streetly) Management Limited | Households | 1998 |
| Oaks Court (51 Temple Road) Company Limited | Households | 1998 |
| Oaks Road Residents Association Limited(The) | Households | 1986 |
| Oaksmith Development Ltd | Construction | 2023 |
| Oakway Flats Management Company Limited | Households | 1989 |
| Oakwood Apartments Management Limited | Households | 2014 |
| Oakwood Court RMC Limited | Households | 2006 |
| Oakwood Farm (Sevenoaks) Management Company Limited | Households | 2014 |
| Oakwood Gate (Leverstock Green) Management Company Limited | Households | 2015 |
| Oakwood Park (Wimborne) Management Company Limited | Households | 2024 |
| Oakwood Premium Care Ltd | Health & social care | 2020 |
| Oakwood Premium Properties Ltd | Real estate | 2022 |
| OAR Consulting Private Limited | Professional & scientific | 2019 |
| Oasis Education Centre Limited | Education | 2020 |
| Oasys Residential Ltd | Real estate | 2021 |
| Oatley Park Management Company Limited | Households | 2015 |
| OBA Consulting Firm Limited | Professional & scientific | 2019 |
| Obelisk House (R.T.M.) Company Ltd | Households | 2004 |
| Obelisk House Limited | Households | 2003 |
| Obetodun London Ltd | Hospitality | 2023 |
| OBI One Refurbs Ltd | Construction | 2025 |
| Obikagroup Limited | Wholesale & retail | 2018 |
| Object-Net Technologies Limited | Information & communication | 2012 |
| Objektum Limited | Administrative & support | 2015 |
| Objektum Modernization Limited | Information & communication | 2011 |
| Obrilo UK Ltd | Wholesale & retail | 2025 |
| OBS Building and Services Ltd | Construction | 2024 |
| Obsecure Ltd | Information & communication | 2021 |
| Observatory Fitness Limited | Households | 1995 |
| Observatory Lodge Management Limited | Households | 1996 |
| Observatory Management Limited | Households | 1994 |
| Obsidian Labs Limited | Manufacturing | 2025 |
| Obylistic Services Limited | Other services | 2021 |
| OC Transport Limited | Transport & logistics | 2015 |
| Occasio Marketing Ltd | Administrative & support | 2023 |
| Occupy Certification Ltd | Education | 2024 |
| Ocean Bay Investments Limited | Real estate | 2016 |
| Ocean Logistics ENT Ltd | Transport & logistics | 2024 |
| Ocean Pearls Group LP | | 2015 |
| Ocean Pearls Properties LP | | 2015 |
| Oceancrest Investment Partners Ltd | Real estate | 2026 |
| Oceanus Swim Limited | Administrative & support | 2017 |
| Ocello Limited | Wholesale & retail | 2023 |
| Ochre Developments Limited | Construction | 2023 |
| Ochre Meadows (Theale) Management Company Limited | Households | 2024 |
| Ocibuk Ltd | Wholesale & retail | 2025 |
| Ockham Newton Limited | Professional & scientific | 2025 |
| Ocoloni Industrial Co., Ltd | Wholesale & retail | 2023 |
| OCR Store Limited | Wholesale & retail | 2014 |
| Ocsia Ltd | Households | 2026 |
| Octane Housing & Development (3) Ltd | Construction | 2024 |
| Octane Housing and Development (2) Ltd | Construction | 2024 |
| Octane Housing and Development Ltd | Construction | 2022 |
| Octn Ltd | Wholesale & retail | 2026 |
| Octo Members Limited | Information & communication | 2024 |
| Odak Properties Limited | Households | 2023 |
| Oddfellows Heights Management Company Ltd | Real estate | 2014 |
| Odera Capital Ltd | Professional & scientific | 2026 |
| ODS Staffing Ltd | Administrative & support | 2022 |
| Odysse Ltd | Transport & logistics | 2020 |
| Oesterhaus Real Estate Ltd | Real estate | 2023 |
| OFC Productions Ltd | Information & communication | 2024 |
| Off-Course Limited | Professional & scientific | 2013 |
| Off-Field Productions Limited | Information & communication | 2025 |
| Offerz.Uk Ltd | Professional & scientific | 2020 |
| Office Interior Contracts Limited | Construction | 2020 |
| Officine International Ltd | Hospitality | 2018 |
| Offset Studio Ltd | Professional & scientific | 2025 |
| OG Vipets Ltd | Other services | 2025 |
| Ogi.Ognyanov Ltd | Transport & logistics | 2016 |
| OGM Limited | Health & social care | 2010 |
| OGY Technologies (UK) Ltd | Information & communication | 2020 |
| OH Cars London Ltd | Administrative & support | 2020 |
| OH Spice Ltd | Hospitality | 2021 |
| OH Transport Ltd | Transport & logistics | 2022 |
| OH Wears Ltd | Wholesale & retail | 2023 |
| Ohana 8 Ltd | Information & communication | 2020 |
| OHE Ltd | Construction | 2016 |
| OHM & Safe Electrical Ltd | Construction | 2023 |
| Ohmico Ltd | Construction | 2020 |
| OIL - Offshore Ltd | Professional & scientific | 2022 |
| OJ World Limited | Construction | 2007 |
| OJ World Properties Ltd | Real estate | 2023 |
| OJC Imaging Limited | Professional & scientific | 2014 |
| OK Carpentry Limited | Manufacturing | 2017 |
| Ok-Staffing Limited | Hospitality | 2021 |
| Okasitu-Rk Ltd | Mining & quarrying | 2023 |
| Okenachi Limited | Real estate | 2025 |