| Orion Managed Facilities Ltd | Professional & scientific | 2024 |
| Orison Services Limited | Wholesale & retail | 2019 |
| Orle Ltd | Wholesale & retail | 2025 |
| Orleans Horn Logistics Limited | Administrative & support | 2024 |
| ORM Services Ltd | Transport & logistics | 2022 |
| Ormino Limited | Wholesale & retail | 2026 |
| ORO Botanica Limited | Manufacturing | 2025 |
| Orphans in Need | Professional & scientific | 2011 |
| Orthodentx Ltd | Health & social care | 2026 |
| Orus Group Ltd | Wholesale & retail | 2023 |
| Oryon International Limited | Wholesale & retail | 2025 |
| Oryx Retail Group Limited | Wholesale & retail | 2019 |
| Oryxxx Limited | Wholesale & retail | 2018 |
| Oryza Wellness Ltd | Other services | 2025 |
| Osama International Ltd | Wholesale & retail | 2022 |
| Oscar Overseas Education Ltd | Education | 2023 |
| Oscare Limited | Information & communication | 2021 |
| Oscorla Limited | Professional & scientific | 2016 |
| Oscrete UK Ltd | Construction | 2021 |
| Oseq Childcare Limited | Health & social care | 2023 |
| Osinso Ltd | Wholesale & retail | 2025 |
| Osmium Security Solutions Ltd | Administrative & support | 2025 |
| Osoap Global Ltd | Wholesale & retail | 2025 |
| Ossaatt Limited | Other services | 2019 |
| Ostalo Ltd | Manufacturing | 2025 |
| Oswalt Tree Services Ltd | Administrative & support | 2025 |
| Oswin Business Solutions Ltd | Professional & scientific | 2026 |
| OTA Services Ltd | Real estate | 2025 |
| OTC Bolton Limited | Hospitality | 2017 |
| Otium Suites Ltd | Real estate | 2023 |
| Otley Civic Centre Limited | Real estate | 2020 |
| Otley Road and Undercliffe Community Works | Other services | 2004 |
| Otter Watersports Limited | Manufacturing | 1999 |
| Ottimo Direct Ltd | Wholesale & retail | 2025 |
| Otto Coffee and Wine Bar Ltd | Hospitality | 2015 |
| Otto Seeger Limited | Professional & scientific | 2017 |
| Ottomans Ltd | Wholesale & retail | 2020 |
| OUD AL Arab Limited | Wholesale & retail | 2019 |
| Oudinair Limited | Manufacturing | 2025 |
| Oula Creative Catering Ltd | Hospitality | 2021 |
| Oula Properties Ltd | Real estate | 2024 |
| OUR BD4 C.I.C. | Education | 2016 |
| OUR Bradford CIC | Education | 2024 |
| OUR Football Academy Limited | Arts & recreation | 2024 |
| OUR Little Angelz (Greengates) Ltd | Health & social care | 2026 |
| OUR Livelihood Limited | Professional & scientific | 2016 |
| OUR Shared Garden Limited | Professional & scientific | 2020 |
| OUR Space Properties Ltd | Hospitality | 2025 |
| OUR Space Respite Ltd | Health & social care | 2025 |
| OUR Women First CIC | Education | 2024 |
| OUT of Place Studio Ltd | Information & communication | 2020 |
| OUT There Group Limited | Information & communication | 2019 |
| Outbox Media Limited | Manufacturing | 2025 |
| Outloud Ltd | Education | 2017 |
| Outout Technologies Ltd | Information & communication | 2025 |
| Outskirts Construction Ltd | Construction | 2025 |
| Outsmart Agency Limited | Professional & scientific | 2009 |
| Outvest Holding Limited | Financial services | 2025 |
| Overland Developments Limited | Construction | 2003 |
| Overland Developments Management Limited | Construction | 2023 |
| Overland Residentials Limited | Real estate | 2018 |
| Overseas United Limited | Wholesale & retail | 2022 |
| OVICOS93 Ltd | Transport & logistics | 2025 |
| Oviya Food and Wine Ltd | Wholesale & retail | 2018 |
| Ovoca Heating Ltd | Construction | 2023 |
| Ovolia Ltd | Water & waste | 2023 |
| Ovrszd Ltd | Wholesale & retail | 2023 |
| OW Contracting Services Ltd | Real estate | 2024 |
| OW Healthcare Limited | Health & social care | 2012 |
| Owenbeg Contracts Ltd | Construction | 2017 |
| OWH BD16 Ltd | Administrative & support | 2016 |
| OWL View Cottage Ltd | Hospitality | 2021 |
| Own a Car Ltd | Information & communication | 2015 |
| Owo-Elepo Foods Ltd | Wholesale & retail | 2025 |
| Oxbridge Mobile Tyre Fitting Ltd | Wholesale & retail | 2023 |
| Oxon Investment 16 Limited | Real estate | 2016 |
| Oxon Maintenance Solutions Ltd | Construction | 2015 |
| OXQ Ltd | Construction | 2025 |
| Oxygen Construction Limited | Construction | 2021 |
| Oxygen Padel Ltd | Arts & recreation | 2025 |
| Oxygen Recovery Ltd | Other services | 2026 |
| OYE Market Limited | Wholesale & retail | 2021 |
| OZ Homewares Ltd | Wholesale & retail | 2024 |
| Ozman Enterprise Limited | Real estate | 2024 |
| Ozua Ltd | Manufacturing | 2024 |
| Ozze Properties Ltd | Real estate | 2019 |
| P & G Solutions Ltd | Financial services | 2017 |
| P & L Industrial Roofing Ltd | Construction | 2013 |
| P & P Property Developments Ltd | Real estate | 2024 |
| P a Foods Yorkshire Limited | Hospitality | 2026 |
| P Akhtar Ltd | Wholesale & retail | 2017 |
| P Aslam Holdings Limited | Financial services | 2023 |
| P C Pipeline Solutions Ltd | Construction | 2014 |
| P D Bannister Haulage Limited | Transport & logistics | 1996 |
| P Dunne and Sons Ltd | Construction | 2007 |
| P F Holding UK Ltd | Hospitality | 2018 |
| P Hansell Window Cleaning Ltd | Administrative & support | 2023 |
| P J H Corporation EOT Ltd | Wholesale & retail | 2025 |
| P M Clayton Transport Services Ltd | Transport & logistics | 2016 |
| P MCR Limited | Hospitality | 2024 |