| Oakridge Arena Ltd | Administrative & support | 2023 |
| Oaktree Property Venture Limited | Professional & scientific | 1998 |
| Oakwood Feeds Ltd | Wholesale & retail | 2020 |
| Oamh Ltd | Professional & scientific | 2013 |
| Oasis Auction Hub Ltd | Wholesale & retail | 2024 |
| Oasis Cafe Ollerton Limited | Hospitality | 2020 |
| OB Plumbing Services Ltd | Construction | 2021 |
| Obsidian Construction Services Ltd | Construction | 2014 |
| Ocean Straits Limited | Wholesale & retail | 2005 |
| Ocellus Risk Ltd | Administrative & support | 2017 |
| Octagon Business Development Ltd | Professional & scientific | 2011 |
| Octopus Coatings Ltd | Manufacturing | 2023 |
| Octopus Developments Ltd | Real estate | 2025 |
| ODD JOB John Ltd | Construction | 2016 |
| OF Many Circles Limited | Professional & scientific | 2019 |
| OFD Projects Limited | Real estate | 2025 |
| Oferto Ltd | Professional & scientific | 2020 |
| Oferto Properties Ltd | Real estate | 2023 |
| Office Angel Book Keeping Ltd | Professional & scientific | 2012 |
| OG Electrical Limited | Construction | 2026 |
| Oggy Cars Ltd | Wholesale & retail | 2026 |
| Oglesbees Limited | Agriculture & fishing | 2019 |
| Ogon Homes Limited | Construction | 2006 |
| OHF Consulting Ltd | Information & communication | 2024 |
| OIL Well 2000 (Holdings) Limited | Professional & scientific | 2014 |
| OIL Well Services 2000 Limited | Construction | 2000 |
| Ojisan Web Development Ltd | Information & communication | 2025 |
| OJZ Engineering Limited | Wholesale & retail | 2006 |
| Old Duck Limited | Hospitality | 2024 |
| Old Farm Harby Limited | Other services | 2025 |
| Old Farm Spa Limited | Other services | 2014 |
| Old Hall RTM 2026 Ltd | Households | 2026 |
| Olec Limited | Construction | 2011 |
| Olive Grove Engineering Solutions Ltd | Administrative & support | 2020 |
| Olive MAE Riddy Limited | Real estate | 2025 |
| Oliver Emmett Limited | Financial services | 2024 |
| Oliver Jones Property Limited | Real estate | 2025 |
| Olivia Paige Dance and Performance Ltd | Arts & recreation | 2022 |
| OLL Newco 102 Limited | Financial services | 2025 |
| Ollerton Continental Foodhub Ltd | Hospitality | 2026 |
| Ollerton Self Storage Ltd | Other services | 2026 |
| Olowofela Ltd | Manufacturing | 2025 |
| Omar and J Ltd | Hospitality | 2024 |
| Onboard Solutions & Sons Ltd | Professional & scientific | 2017 |
| Onebigstar (Holdings) Limited | Financial services | 2018 |
| Onebigstar Limited | Administrative & support | 2011 |
| Onemorefortheroad Ltd | Hospitality | 2020 |
| Onshore Oilfield Services Limited | Mining & quarrying | 1996 |
| Onshore Petroleum Limited | Mining & quarrying | 2017 |
| Onshore Production Services Limited | Mining & quarrying | 2001 |
| Oojerfink Ltd | Information & communication | 2026 |
| OP Talent Management Limited | Professional & scientific | 2023 |
| Opal HR Limited | Professional & scientific | 2014 |
| Open Design Systems Ltd | Information & communication | 2004 |
| Open Door Retail Consultancy Limited | Professional & scientific | 2026 |
| OPR Estates Ltd | Real estate | 2020 |
| Optic Creative Ltd | Professional & scientific | 2015 |
| Optimise Systems Ltd | Information & communication | 2004 |
| Optimum Results Ltd | Health & social care | 2023 |
| Optimus Architectural Ltd | Construction | 2014 |
| Optique Vision (Collingham) Limited | Wholesale & retail | 2025 |
| Oramoss Limited | Information & communication | 1996 |
| Orange Media Productions Ltd | Professional & scientific | 2015 |
| Orange Supply Chain Limited | Professional & scientific | 2018 |
| Orca Estates Limited | Real estate | 2020 |
| Orchard Grove East Markham Management Company Limited | Real estate | 2017 |
| Orchard House Projects Limited | Real estate | 2003 |
| Order Pet Food Limited | Wholesale & retail | 2020 |
| Oricull Limited | Professional & scientific | 2025 |
| Orka Transformer Services Limited | Construction | 2020 |
| Ormsby Property Ltd | Real estate | 2020 |
| ORTOM8 Limited | Information & communication | 2020 |
| ORW Properties Limited | Real estate | 2018 |
| Orwood Independent Living Limited | Manufacturing | 2017 |
| Orwood Mobility Manufacturing Limited | Manufacturing | 2019 |
| Osrc Ltd | Administrative & support | 2021 |
| Otter Psychology Ltd | Health & social care | 2026 |
| Otterganics Ltd | Wholesale & retail | 2018 |
| Ottimo Projects Ltd | Real estate | 2026 |
| Over the Moon Limited | Hospitality | 2009 |
| Overhead Reduction Specialists Limited | Professional & scientific | 2004 |
| Overwrought Ironwork Limited | Manufacturing | 2003 |
| Owed Limited | Professional & scientific | 2013 |
| OWG Engineering Limited | Professional & scientific | 2026 |
| Oxedio CE Property Ltd | Professional & scientific | 2021 |
| OXO House Associates Limited | Professional & scientific | 2015 |
| Ozog&Son Limited | Transport & logistics | 2024 |
| P & a Croft (Farmers) Limited | Agriculture & fishing | 2003 |
| P & a Mining Machinery Services Limited | Manufacturing | 2014 |
| P & D Collections Limited | Administrative & support | 2021 |
| P a Davies Electrical Limited | Construction | 2011 |
| P C Tutor Services Ltd | Education | 2016 |
| P Crosby Limited | Construction | 2007 |
| P G W Field Maintenance Limited | Manufacturing | 2020 |
| P M Bradley Fabrications Limited | Manufacturing | 2002 |
| P T Shirts Limited | Professional & scientific | 2007 |
| P W Well (Holdings) Limited | Professional & scientific | 2014 |
| P W Well Services Limited | Mining & quarrying | 2003 |
| P W Well Test Limited | Mining & quarrying | 2014 |
| P.A. Freight Services (Midlands) Limited | Transport & logistics | 1988 |