| Offoxey Road Limited | Real estate | 2021 |
| Offsight IT Services Limited | Information & communication | 2004 |
| OG Technology Ltd | Wholesale & retail | 2021 |
| OH My GOD Limited | Hospitality | 2007 |
| Ohana Hair (Brewood) Limited | Other services | 2021 |
| OJS Heating & Air Conditioning Limited | Construction | 2025 |
| Okra Spice Dinning Limited | Hospitality | 2026 |
| OKTAN88 Limited | Hospitality | 2020 |
| Olawunmis Childcare Limited | Health & social care | 2024 |
| Old Crown Mews Management Co Ltd | Households | 2024 |
| Old Hall Barns Management Company Limited | Households | 2007 |
| Old Stables Ingestre (Maintenance) Limited(The) | Households | 1979 |
| Old Surgery (Pinfold Lane) Management Limited | Households | 2021 |
| Oldroyd Guest House (2009) Limited | Hospitality | 2009 |
| Olive Housing Solutions Limited | Real estate | 2023 |
| Olive Smile Solutions Limited | Health & social care | 2023 |
| Oliver Deakin Limited | Wholesale & retail | 2025 |
| Olivia Antonina Ltd | Professional & scientific | 2025 |
| Olivia Dash Limited | Health & social care | 2023 |
| Olivia Rose Pilates Ltd | Education | 2024 |
| Olivia Rose Pilates Studio Limited | Arts & recreation | 2024 |
| Olmoll Limited | Administrative & support | 2025 |
| Omaha Trading Co., Ltd | Manufacturing | 2022 |
| OMC Tamworth Home Ltd | Extraterritorial | 2023 |
| Omiab Consultancy Limited | Professional & scientific | 2026 |
| Omicron Electronics UK Limited | Wholesale & retail | 1999 |
| Omishine EU Limited | Wholesale & retail | 2021 |
| Omix Limited | Professional & scientific | 2023 |
| Omnivarya Limited | Wholesale & retail | 2025 |
| ON Tour Transport Limited | Transport & logistics | 2005 |
| One 2 Pass Driving School Ltd | Education | 2018 |
| One CE Testing (Yiwu) Co., Ltd | Wholesale & retail | 2024 |
| One Last Round Vodka Ltd | Manufacturing | 2021 |
| One World Peace Co., Ltd | Financial services | 2022 |
| Oneharmony Media Ltd | Wholesale & retail | 2025 |
| Onetocare Services Ltd | Health & social care | 2022 |
| Online for Equine Limited | Wholesale & retail | 2012 |
| Onlycams UK Limited | Wholesale & retail | 2022 |
| Onlyfins Limited | Wholesale & retail | 2023 |
| Onyx Collaborative Social Work Services Ltd | Health & social care | 2026 |
| Onyx Newsroom Ltd | Professional & scientific | 2023 |
| Opalight Solutions Limited | Wholesale & retail | 2024 |
| Opalite Cleaning Services Limited | Administrative & support | 2025 |
| Open LET Limited | Real estate | 2021 |
| Opensky Academy Ltd | Education | 2025 |
| Operation Removal Ltd | Transport & logistics | 2025 |
| Opgen Ltd | Manufacturing | 2023 |
| OPM Tech Ltd | Energy | 2014 |
| Opti-Print Ltd | Manufacturing | 2026 |
| Optima Warehouse Solutions Limited | Information & communication | 2001 |
| Optimise Worldwide Ltd | Wholesale & retail | 2026 |
| Optimum Building and Project Consultancy Limited | Professional & scientific | 2007 |
| Opuseng Ltd | Administrative & support | 2013 |
| Orange Technology and Science Ltd | Wholesale & retail | 2021 |
| Orange UNI Pads Limited | Real estate | 2015 |
| Orbis Engineering Services Ltd | Construction | 2014 |
| Orbis EV Limited | Construction | 2021 |
| Orbit Healthcare Recruitment Ltd. | Health & social care | 2020 |
| Ordinary Classrooms Education Consultancy Ltd | Education | 2019 |
| Organic Natural Ltd | Manufacturing | 2025 |
| Orient Industry Co., Ltd | Extraterritorial | 2021 |
| Oriental Stafford Limited | Hospitality | 2017 |
| Orion E Commerce Ltd | Wholesale & retail | 2025 |
| ORJ Law Limited | Professional & scientific | 2018 |
| ORJ Solicitors LLP | | 2004 |
| Orlik Drive Limited | Administrative & support | 2019 |
| Orqa Software Ltd | Information & communication | 2024 |
| Orson Power Limited | Manufacturing | 2024 |
| Osier Technology Consultants Ltd | Information & communication | 2020 |
| Ostling Etch-Mark Limited | Manufacturing | 2008 |
| Othereye Ltd | Other services | 2019 |
| Otherton Hall Farm Management Company Limited | Households | 2018 |
| Otoole Vintage Ltd | Wholesale & retail | 2022 |
| OTS Secretarial Limited | Extraterritorial | 2013 |
| Oughton Group Ltd | Financial services | 2024 |
| Oughton TV & Film Services Limited | Information & communication | 2022 |
| Oulimeiting Daily Necessities Co., Ltd | Wholesale & retail | 2025 |
| Oulton GAS Services Ltd | Construction | 2023 |
| Oulton House Farm Limited | Agriculture & fishing | 2008 |
| OUR Local Business Limited | Information & communication | 2020 |
| Ourlove Limited | Information & communication | 2025 |
| Outback HOG Roasts Limited | Hospitality | 2004 |
| Outbreak Ltd | Administrative & support | 2017 |
| Outré Ltd | Wholesale & retail | 2022 |
| Outserve Limited | Information & communication | 2008 |
| Ovalside Court (Maintenance) Limited | Households | 1986 |
| Oversea Sailing Media Ltd | Wholesale & retail | 2025 |
| Overseas ARK Ltd | Wholesale & retail | 2025 |
| Owen James Morgan | Extraterritorial | 2024 |
| Owen Thomas Cotton Apparel Ltd | Wholesale & retail | 2026 |
| Oxentech Trading Ltd | Wholesale & retail | 2025 |
| Oxford Plame Limited | Wholesale & retail | 2025 |
| Oxford Tax Solutions Limited | Professional & scientific | 2009 |
| OXI Partition Ltd | Construction | 2019 |
| Oxleasows Enterprises Ltd | Agriculture & fishing | 2021 |
| Oxygen Media Ltd | Information & communication | 2018 |
| Oyster Residential Ltd | Real estate | 2006 |
| P & G Rail Consulting Limited | Professional & scientific | 2017 |
| P & N Farming Limited | Extraterritorial | 2005 |
| P & R Jones Tree Services Limited | Construction | 2010 |