| Opal Hotel Collection Holdings Ltd | Real estate | 2019 |
| Opal Hotel Collection Ltd | Hospitality | 2019 |
| Operation Worldwide Ltd | Arts & recreation | 2024 |
| Operations Decarbonisation Solutions Limited | Professional & scientific | 2025 |
| OPS First Consultancy Ltd | Professional & scientific | 2024 |
| Optechuk Ltd | Information & communication | 2025 |
| Optichain Ltd | Professional & scientific | 2025 |
| Optimise Capital Limited | Professional & scientific | 2015 |
| Optimise Car Finance Ltd | Financial services | 2025 |
| Optimise Equity Release Ltd | Financial services | 2025 |
| Optimise Finance Limited | Financial services | 2004 |
| Optimise Loans Ltd | Financial services | 2025 |
| Optimise Money Group Limited | Financial services | 2025 |
| Optimise Mortgages Ltd | Financial services | 2025 |
| Optimise Tax Refunds Ltd | Professional & scientific | 2025 |
| Optimised Accounting Limited | Professional & scientific | 2025 |
| Optimised Admin Ltd | Professional & scientific | 2025 |
| Optimised Power Products Ltd | Professional & scientific | 2013 |
| Optimum Projects (UK) Limited | Wholesale & retail | 1996 |
| Optymisr Limited | Professional & scientific | 2025 |
| Opus Business Media Limited | Information & communication | 2009 |
| Opus Technical Limited | Manufacturing | 2012 |
| Orange Baron Properties Limited | Real estate | 2021 |
| Orbital RPA Limited | Professional & scientific | 2022 |
| Orca Medical Communications Limited | Professional & scientific | 2025 |
| Orchard Consultants Ltd | Education | 2016 |
| Orchard Gate (Otley) Limited | Real estate | 2026 |
| Orchard Home Interiors Limited | Wholesale & retail | 2021 |
| Orchard Structural Design Ltd | Administrative & support | 2017 |
| Orchardlea Psychology Limited | Health & social care | 2023 |
| Order DOT Beer Limited | Wholesale & retail | 2017 |
| Ordsgn Ltd | Professional & scientific | 2017 |
| Origin Wholefoods Limited | Hospitality | 2016 |
| Orkney Property Management Limited | Construction | 2022 |
| Ormerods Holdings Limited | Professional & scientific | 2004 |
| Ormerods Limited | Manufacturing | 1919 |
| Orogenesis Ltd | Professional & scientific | 2008 |
| Oscar Compliance Solutions Ltd | Professional & scientific | 2019 |
| Osman Food 68 Ltd | Hospitality | 2026 |
| Osmanlar 68 Ltd | Hospitality | 2025 |
| Osmar Educational Network Ltd | Education | 2025 |
| Osmar Health Care Recruitment Ltd | Health & social care | 2025 |
| OSN Construction and Joinery Ltd | Construction | 2025 |
| OSO Eats Ltd | Hospitality | 2025 |
| Ouitech Ltd | Information & communication | 2020 |
| Oulton Lowe Farms Limited | Agriculture & fishing | 2019 |
| OUR Lady Help of Christians Catholic Academy Trust | Education | 2012 |
| Ours Capital Ltd | Professional & scientific | 2026 |
| OUT in the Sticks C.I.C. | Education | 2024 |
| Outdoor & Sports Company Limited | Manufacturing | 1970 |
| Outdoor Accessories Limited | Wholesale & retail | 2013 |
| Outdoor Active Holdings Limited | Other services | 2024 |
| Outfoxed Films Ltd | Information & communication | 2020 |
| Outreach Marketing Limited | Information & communication | 2018 |
| Outvara Limited | Information & communication | 2026 |
| Outwoodcare Limited | Manufacturing | 2008 |
| Oven Clean (Ontario) Limited | Extraterritorial | 2012 |
| Oven Clean Domestic Limited | Administrative & support | 2003 |
| Overtone Post Production LLP | | 2024 |
| Owlhurst Management Limited | Administrative & support | 1999 |
| Owner Driver Services Ltd | Professional & scientific | 2019 |
| Oxhey Developments Limited | Real estate | 1998 |
| O’Connor Commerce Ltd | Wholesale & retail | 2025 |
| P & N Development & Investments Ltd | Construction | 2015 |
| P Dean Builders & Groundworks Limited | Construction | 2011 |
| P Dean Timber Products Limited | Manufacturing | 2024 |
| P G Barnes Building & Joinery Ltd | Construction | 2014 |
| P H Labels Ltd | Wholesale & retail | 1997 |
| P J Jackson Plant Hire Limited | Administrative & support | 1999 |
| P K Expediting Services Limited | Professional & scientific | 2008 |
| P Walker Flooring Ltd | Construction | 2023 |
| P Woodhouse Properties Ltd. | Real estate | 2017 |
| P&R Horizons Limited | Real estate | 2016 |
| P&S Group of Companies Limited | Manufacturing | 2026 |
| P.A.P Executive Travel (UK) Limited | Transport & logistics | 2018 |
| P.D. (Holdings) Limited | Extraterritorial | 1999 |
| P.D.Business Services Ltd | Professional & scientific | 2006 |
| P.R.B Aerotech Ltd | Manufacturing | 2022 |
| Paalam Consultancy Ltd | Information & communication | 2021 |
| Pachamama and the Seven Rays Ltd | Wholesale & retail | 2021 |
| Paediatric Neurology Consultant Ltd | Health & social care | 2021 |
| Page Mercer EXP Limited | Real estate | 2026 |
| Painters Supply Limited | Wholesale & retail | 2018 |
| Palmerston Developments Ltd | Real estate | 2022 |
| Palmerston Services LLP | | 2017 |
| Palmerston Street Properties Ltd | Real estate | 2020 |
| Palovice.Digital Ltd | Information & communication | 2019 |
| PAM Hulme & Company Limited | Professional & scientific | 2009 |
| Pamoja Education Limited | Education | 2009 |
| Panacea Wellbeing Limited | Health & social care | 2024 |
| Panda Holding Co. Limited | Financial services | 2020 |
| Panton Street Developments Limited | Construction | 2025 |
| PAP Executive Travel Limited | Transport & logistics | 2019 |
| Paprika Dining Ltd | Hospitality | 2022 |
| Parable Holdings Limited | Information & communication | 2021 |
| Paradigm Property Solutions Ltd | Real estate | 2015 |
| Paradise Court (Macclesfield) Management Company Limited | Households | 2019 |
| Paramount Financial Limited | Extraterritorial | 2014 |
| Paris Club Ltd | Agriculture & fishing | 2014 |
| Park Green Car Sales Ltd | Wholesale & retail | 2011 |