| ON the Go Haulage Ltd | Transport & logistics | 2021 |
| On-Site Pool Linings Limited | Construction | 2012 |
| Onari Corporate Limited | Manufacturing | 2017 |
| Ondemand Group Ltd | Transport & logistics | 2025 |
| Ondrives Aerospace Gears Limited | Professional & scientific | 2017 |
| Ondrives Aerospace Limited | Professional & scientific | 2017 |
| Ondrives Gears Limited | Professional & scientific | 2017 |
| Ondrives Group Limited | Professional & scientific | 2012 |
| Ondrives Limited | Manufacturing | 1995 |
| Ondrives PCT Ltd | Manufacturing | 2022 |
| Ondrives Precision Cutting Tools Ltd | Manufacturing | 2022 |
| Ondrives Precision Gears Ltd | Manufacturing | 2022 |
| Ondrives Tools Ltd | Manufacturing | 2022 |
| One Construction and Building Group Ltd | Construction | 2017 |
| One Digital Creations Ltd | Information & communication | 2024 |
| One Great Northern Ltd | Professional & scientific | 2019 |
| One to One Support Services Limited | Health & social care | 2006 |
| One to One Training Academy Limited | Education | 2025 |
| Onehashtag Ltd | Professional & scientific | 2026 |
| Onetech Engineering Ltd | Manufacturing | 2010 |
| Oneway Commercials Limited | Extraterritorial | 2013 |
| Onions Sushi Limited | Hospitality | 2024 |
| Online Golf Limited | Wholesale & retail | 2025 |
| Online Specials Ltd | Wholesale & retail | 2016 |
| Only London Markets Limited | Wholesale & retail | 2018 |
| Onlygames Ltd | Arts & recreation | 2021 |
| Ontaro Limited | Information & communication | 2022 |
| Ontek Limited | Professional & scientific | 1994 |
| Onza Aztec Ltd | Real estate | 2023 |
| Onza Garden Design Ltd | Administrative & support | 2025 |
| Opal Financial Planning Ltd | Professional & scientific | 2020 |
| Opslogic Solutions Ltd | Information & communication | 2026 |
| Opti List Ltd | Real estate | 2018 |
| Optima Consumer Credit Limited | Financial services | 2003 |
| Optimis (Midlands) Ltd | Construction | 2017 |
| Optimise Business Solutions Limited | Other services | 2012 |
| Opus Plumbing and Heating Limited | Construction | 2019 |
| Oracle Trading Limited | Wholesale & retail | 2025 |
| Orca Access Services Ltd | Manufacturing | 2012 |
| Orchard Properties (Chesterfield) Limited | Real estate | 2004 |
| Orchid Noir Beauty Ltd | Other services | 2020 |
| ORD Surveying Limited | Construction | 2022 |
| Ordobot Ltd | Information & communication | 2026 |
| Original Gravity Beers Ltd | Wholesale & retail | 2024 |
| Ornate Stoneware Limited | Manufacturing | 2012 |
| ORO Estates Limited | Real estate | 2024 |
| Oscar Lets Limited | Real estate | 2026 |
| Ossian Capital Limited | Financial services | 2013 |
| Ossian Homes Limited | Construction | 2019 |
| Ossian Property Management Limited | Real estate | 2019 |
| OTI Group Limited | Information & communication | 2025 |
| OTI Interiors Ltd | Manufacturing | 2020 |
| OTL Consulting Limited | Professional & scientific | 2018 |
| Oval Trading Limited | Wholesale & retail | 1998 |
| Ovation Limited | Information & communication | 2001 |
| Oven Fresh and Carpet Fresh Limited | Other services | 2012 |
| Overton Estate Farm Limited | Agriculture & fishing | 2012 |
| Overton Water Community Interest Company | Water & waste | 2023 |
| OW DO Cafe and Bar Limited | Hospitality | 2025 |
| Owen Consultancy Ltd | Information & communication | 2021 |
| Owen Hardy Limited | Professional & scientific | 2023 |
| Owen's Car & Commercial Ltd | Wholesale & retail | 2007 |
| OWL Bidco Limited | Financial services | 2020 |
| OWL Property Care Limited | Health & social care | 2020 |
| Oxbys Holdings Ltd | Real estate | 2025 |
| Oxcroft HR Consulting Limited | Administrative & support | 2022 |
| Oxdale Products Limited | Manufacturing | 2008 |
| Oxdale Properties Limited | Real estate | 2021 |
| Oxford Clothes Hub CIC | Wholesale & retail | 2023 |
| Oxley Mortgage Solutions Ltd | Financial services | 2025 |
| Oxnames Ltd | Information & communication | 2020 |
| Oxpark Limited | Wholesale & retail | 2020 |
| Oxyclinic Ltd | Health & social care | 2025 |
| Oxyhealthcare Mansfield Ltd | Health & social care | 2025 |
| P & B Health & Safety Solutions Ltd | Professional & scientific | 2004 |
| P & D Leisure Limited | Hospitality | 2015 |
| P & H Dalton Properties Limited | Households | 2026 |
| P & J Builders (Chesterfield) Ltd | Construction | 2013 |
| P & M Coaching Ltd | Education | 2024 |
| P & R Couriers Ltd | Transport & logistics | 2023 |
| P a S Decorators Ltd | Construction | 2003 |
| P and M Electrical Control and Automation Limited | Manufacturing | 2004 |
| P B Environmental Services Limited | Professional & scientific | 2007 |
| P E Weldright Limited | Construction | 2009 |
| P H Coates Ltd | Financial services | 2006 |
| P J Downs Gardening Services Ltd | Administrative & support | 2023 |
| P J Fire Limited | Manufacturing | 2007 |
| P J Reynolds (Midlands) Limited | Wholesale & retail | 2015 |
| P K Electrical Limited | Construction | 2001 |
| P Parker & SON Limited | Transport & logistics | 2004 |
| P R Engineering Limited | Wholesale & retail | 1994 |
| P R Marriott Drilling Limited | Construction | 1991 |
| P S Rutland Management Services Limited | Financial services | 2015 |
| P S Wilkinson Building Services Limited | Construction | 2006 |
| P Turner Erections Limited | Construction | 1963 |
| P Turton Building & Conservation Ltd | Construction | 2012 |
| P V Private Limited | Health & social care | 2014 |
| P Walt Ltd | Transport & logistics | 2025 |
| P Wilson Build Limited | Construction | 2023 |
| P&A DOM Limited | Real estate | 2025 |