| Options Hospitality Services Ltd | Hospitality | 2019 |
| Options Property Services Ltd | Real estate | 2019 |
| Opus Search Limited | Administrative & support | 2013 |
| Oranjade Ltd | Administrative & support | 2020 |
| Orchard Cottage Properties Limited | Real estate | 2015 |
| Orchard Grange Residents Association Limited | Households | 2002 |
| Orchard Holdings (Landbeach) Limited | Other services | 2018 |
| Orchard Linen Hire Limited | Other services | 2018 |
| Orchid Close (Luton) Management Company Limited | Households | 2006 |
| Orchidcache Systems Ltd | Information & communication | 2016 |
| Orebs Incorporations Limited | Health & social care | 2009 |
| Oriental Consultancy Limited | Information & communication | 2002 |
| Original Tech Accessories Ltd | Wholesale & retail | 2021 |
| Orion Safety Belts Limited | Manufacturing | 2002 |
| ORJ Investments Ltd | Real estate | 2021 |
| ORL - Medical Ltd | Health & social care | 2022 |
| Ormonde Creative Limited | Information & communication | 2025 |
| Orovela Ltd | Real estate | 2019 |
| Orral Properties Ltd | Construction | 2026 |
| Orthopaedic Hands Ltd | Education | 2024 |
| Ortonatura Viva Ltd | Wholesale & retail | 2019 |
| Orwell House Limited | Households | 2007 |
| Oscar Heat & Plumbing Ltd | Construction | 2025 |
| Oscmar Consulting Ltd | Construction | 2022 |
| OSE Clinical Rehabilitation & OT Consultancy Limited | Administrative & support | 2026 |
| Osen Healthcare Ltd. | Health & social care | 2015 |
| Osprey Cleaning Group Ltd | Administrative & support | 2026 |
| Osprey Homes (Central) Limited | Construction | 2017 |
| Osprey Homes (Eastern) Limited | Construction | 2017 |
| Osprey Homes (South East) Limited | Construction | 2011 |
| Osprey Homes (South) Limited | Construction | 2013 |
| Osprey Homes Limited | Construction | 2014 |
| Osteopathy at Home Limited | Health & social care | 2017 |
| Osteopathy on Animals Limited | Professional & scientific | 2017 |
| Ostozhenka Holdings | Financial services | 2024 |
| Otaya Property Ltd | Real estate | 2019 |
| Otca Limited | Construction | 2018 |
| Otec Service Solutions Limited | Other services | 2017 |
| Oten Engineering Ltd | Professional & scientific | 2018 |
| Otis B Ltd | Professional & scientific | 2021 |
| Otter Engineering Services Ltd | Professional & scientific | 2014 |
| Ottiche Network Solutions Limited | Information & communication | 2014 |
| Ottimo Stevenage Limited | Hospitality | 2024 |
| Ourkid Talent Ltd | Arts & recreation | 2025 |
| Outcomes Based Healthcare Ltd | Information & communication | 2013 |
| Outer London Surfacing Ltd | Construction | 2011 |
| Outline Pictures Limited | Information & communication | 2018 |
| Outspoken Media Limited | Information & communication | 2002 |
| Ouzel Consultancy Ltd | Information & communication | 2011 |
| Ouzel Properties Ltd | Real estate | 2022 |
| Oval Academy Limited | Education | 2024 |
| Ovastyle Limited | Wholesale & retail | 2025 |
| Oven Sparkle Stevenage Ltd | Other services | 2015 |
| Over Healthcare Limited | Wholesale & retail | 2010 |
| Overbrook Ltd | Information & communication | 2019 |
| Overbrook Property Services Ltd | Real estate | 2023 |
| Overleaf Property Search Limited | Real estate | 2023 |
| Oxbridge International College Limited | Education | 2022 |
| Oxbridge Professional Training Centre UK Limited | Education | 2009 |
| Oxbury Property LLP | | 2009 |
| Oxenham Associates Limited | Professional & scientific | 1993 |
| Oxford EYE Associates Limited | Health & social care | 2025 |
| Oxford Genelab Academy Ltd | Professional & scientific | 2021 |
| Oxley Dental Limited | Health & social care | 2014 |
| OZ Fish & Chips Ltd | Hospitality | 2025 |
| OZ Kebab Ltd | Hospitality | 2023 |
| Oziclean Ltd | Administrative & support | 2021 |
| Ozpol Ltd | Other services | 2022 |
| O’Keeffe Roofing Ltd | Construction | 2022 |
| P & D Electrical Contractors Limited | Construction | 2018 |
| P & K Group Limited | Financial services | 2026 |
| P & P (Contract Management) Limited | Professional & scientific | 1997 |
| P & P Associates Ltd | Administrative & support | 1987 |
| P & P Consultants Ltd | Construction | 2020 |
| P & P Dwellings Ltd | Real estate | 2023 |
| P & P HR and Quality Services Ltd | Administrative & support | 2023 |
| P & S Williams Refrigeration Limited | Manufacturing | 1993 |
| P Controls 21 Limited | Professional & scientific | 2021 |
| P E N Enterprise Limited | Other services | 2008 |
| P J Andrews Services Limited | Construction | 2003 |
| P March Builders Limited | Construction | 2024 |
| P N Enterprises Limited | Other services | 2014 |
| P&L Construct Ltd | Construction | 2017 |
| P&Mconsultants Ltd | Administrative & support | 2020 |
| P&P Fulfilment Ltd | Administrative & support | 2006 |
| P&P Group Limited | Administrative & support | 2007 |
| P. Shah Ltd | Professional & scientific | 2022 |
| P.J.Simpson Electrical Ltd | Other services | 2017 |
| P.Rose Electrical Limited | Construction | 2025 |
| P2P Solutions Ltd | Information & communication | 2025 |
| PA Soft Drinks Limited | Wholesale & retail | 2025 |
| Paarth and Agastya Health and Wellbeing Limited | Health & social care | 2024 |
| Pacemaker Productions Ltd | Information & communication | 2022 |
| Pacetec Limited | Manufacturing | 2015 |
| Pacific Coast Ltd | Real estate | 2016 |
| Pack & Dash Ltd | Transport & logistics | 2025 |
| Pack Leader Limited | Other services | 2020 |
| Padel Time Ltd | Arts & recreation | 2025 |
| Padel Travel Company Ltd | Administrative & support | 2025 |
| Padel Zone Ltd | Arts & recreation | 2025 |