| OM Search Consultants Ltd | Administrative & support | 2023 |
| Omaa Trade Ltd | Wholesale & retail | 2025 |
| Omado Ltd | Health & social care | 2023 |
| Omap & Co Ltd | Wholesale & retail | 2019 |
| Omap & Co Stourport Limited | Wholesale & retail | 2023 |
| Omap & Co Suites Ltd | Administrative & support | 2024 |
| Omap Property Ltd | Real estate | 2022 |
| OMG Kaptins Limited | Hospitality | 2024 |
| OMG Phat Jackets Ltd | Hospitality | 2025 |
| Ommersys Ltd | Professional & scientific | 2025 |
| OMNI8 Limited | Information & communication | 2025 |
| Omnicare Nexus Limited | Health & social care | 2026 |
| Omninest Trading Ltd | Wholesale & retail | 2025 |
| Omnix Mart Ltd | Wholesale & retail | 2025 |
| Omoruyi Limited | Wholesale & retail | 2025 |
| Omsparts Ltd | Wholesale & retail | 2019 |
| Omteejay Ltd | Professional & scientific | 2015 |
| ON Call Group Resources Ltd | Administrative & support | 2009 |
| ON Call Technical Support Limited | Administrative & support | 2020 |
| ON Call Utilities Ltd | Administrative & support | 2000 |
| ON Point Roofing Contractors Ltd | Construction | 2019 |
| ON the Ball Travel Ltd | Administrative & support | 2012 |
| ON the Go Property Management Limited | Real estate | 2020 |
| ON the Go Traffic Management Limited | Administrative & support | 2017 |
| ON Time Haze Ltd | Transport & logistics | 2018 |
| Onboard (Holdings) Limited | Financial services | 2019 |
| Onboard Corrugated Limited | Manufacturing | 2010 |
| Onboard Investments Limited | Real estate | 2013 |
| Onbrand Merchandise Limited | Professional & scientific | 2013 |
| Oncall Group Security Ltd | Administrative & support | 2014 |
| One Footstep | Education | 2016 |
| One Furniture Outlet Ltd | Wholesale & retail | 2024 |
| One Goodwood Limited | Financial services | 2021 |
| One Haven CIC | Administrative & support | 2025 |
| One Home Care Services Ltd | Health & social care | 2022 |
| One Housing Ltd | Real estate | 2021 |
| One Jerk Stop Ltd | Hospitality | 2023 |
| One Meadow Ltd | Real estate | 2026 |
| One Multi Academies Trust Limited | Education | 2011 |
| One Oak (ALB) Limited | Construction | 2022 |
| One Oak (Lich) Limited | Construction | 2022 |
| One Percent Club Perfume Ltd | Wholesale & retail | 2024 |
| One Shot Cafe Limited | Hospitality | 2024 |
| One Stop Afro Caribbean Ltd | Wholesale & retail | 2025 |
| One Stop Barbers Ltd | Other services | 2025 |
| One Stop Healthcare Ltd | Wholesale & retail | 2016 |
| One Stop Maintenance OSM Ltd | Construction | 2007 |
| One Stop Spring Road Limited | Wholesale & retail | 2015 |
| One UP Financial Group Ltd | Financial services | 2024 |
| One Wolf Consulting Ltd | Professional & scientific | 2019 |
| One Wolverhampton Ltd | Wholesale & retail | 2025 |
| Onecare World Health Limited | Health & social care | 2022 |
| Onecnc UK Limited | Information & communication | 2003 |
| Oneness Autos Limited | Wholesale & retail | 2023 |
| Oneplusthree Cleaning Solutions Ltd | Administrative & support | 2025 |
| Ongar Fyfield Park Real Estate Limited | Real estate | 2024 |
| Onis Group Ltd | Information & communication | 2025 |
| Onka UK Electrical Ltd | Wholesale & retail | 2024 |
| Onkarkitekt Ltd | Real estate | 2021 |
| Online and Deliveriez Limited | Hospitality | 2026 |
| Online Boiler Services Limited | Other services | 2020 |
| Online Fruit & Veg.Com Limited | Wholesale & retail | 2021 |
| Online Interns Ltd | Education | 2022 |
| Online Plant Sales Limited | Wholesale & retail | 2016 |
| Online Quran College Ltd | Education | 2026 |
| Online Safety Solutions Limited | Administrative & support | 2004 |
| Online Vape Shop Ltd | Wholesale & retail | 2024 |
| Only Depot Ltd | Wholesale & retail | 2019 |
| ONM Construction Ltd | Construction | 2022 |
| Onpoint Property Improvements Ltd | Construction | 2025 |
| Ontrac Writer Ltd | Information & communication | 2025 |
| Onxra Limited | Administrative & support | 2025 |
| Onyx Accountants West Ltd | Professional & scientific | 2006 |
| Onyx Coaching Ltd | Health & social care | 2023 |
| Onyx Racing Limited | Wholesale & retail | 2020 |
| Opac Limited | Wholesale & retail | 2010 |
| Opal Envelopes Limited | Manufacturing | 1991 |
| Opal Planning and Property Services Ltd | Real estate | 2026 |
| Opel Management Services Ltd | Professional & scientific | 2016 |
| Open Arms Homes CIC | Health & social care | 2025 |
| Open Hands Psychology Ltd | Education | 2025 |
| Open LAB Technologies Ltd | Information & communication | 2024 |
| Open Road Learning Limited | Professional & scientific | 2004 |
| Opengate Properties Limited | Real estate | 2020 |
| Opening Doors Property Limited | Real estate | 2020 |
| Openmarket Ventures Ltd | Wholesale & retail | 2026 |
| Operated Access Limited | Construction | 2016 |
| Opes Planners Limited | Professional & scientific | 2025 |
| Opeth Properties Limited | Real estate | 2025 |
| Oponee Consulting and Construction Ltd | Construction | 2020 |
| Opta 1 Limited | Construction | 2024 |
| Optical Data Services Ltd | Information & communication | 2017 |
| Optical Network Services Limited | Information & communication | 2016 |
| Opticom Ltd | Information & communication | 2023 |
| Optima Contracts Ltd | Construction | 2015 |
| Optimised Care Asset Limited | Public administration | 2025 |
| Optimize Marketing Ltd | Professional & scientific | 2025 |
| Optimum Contracts Limited | Construction | 2007 |
| Optimus Clicks Ltd | Wholesale & retail | 2023 |
| Opulence DSR Ltd | Real estate | 2026 |