| OPS Trade Masters Ltd | Wholesale & retail | 2025 |
| Optimistic Homes Limited | Real estate | 2025 |
| Optimum Research and Consultancy Ltd | Administrative & support | 2017 |
| Optiscript Limited | Health & social care | 2025 |
| Optizen Consultancy Limited | Professional & scientific | 2023 |
| Opus Staffing Ltd | Administrative & support | 2025 |
| ORA Solutions Limited | Professional & scientific | 2022 |
| Orbit Cars Limited | Transport & logistics | 2023 |
| Orbit Light Creation Ltd | Wholesale & retail | 2025 |
| Orchard Global Consultancy Limited | Professional & scientific | 2016 |
| Oreo Property Ltd | Households | 2021 |
| Organic Able Body Limited | Manufacturing | 2026 |
| Organic Life Products Ltd | Wholesale & retail | 2024 |
| Organic Scenes Limited | Construction | 2025 |
| Organisation of Hindu Malayalees UK CIC | Health & social care | 2026 |
| Orient College in London Ltd | Education | 2024 |
| Original Cloves Indian Takeaway Ltd | Hospitality | 2018 |
| Originial Ltd | Wholesale & retail | 2025 |
| Orivexasearch Limited | Administrative & support | 2026 |
| Oros Services Ltd | Transport & logistics | 2021 |
| Orra Revitalise Ltd | Manufacturing | 2025 |
| Orthoticare (PVT) Ltd | Real estate | 2014 |
| Oruci Coffee Bar Ltd | Hospitality | 2020 |
| OS Homes Ltd | Real estate | 2022 |
| Os-Link Ltd | Information & communication | 2011 |
| Osariemen & Associates Limited | Professional & scientific | 2025 |
| Osaro Limited | Construction | 2017 |
| OSC Jasmine Limited | Health & social care | 2014 |
| Oscar J Ventures Limited | Health & social care | 2023 |
| Oscar Safety Consultants Limited | Professional & scientific | 2018 |
| Osdan Ventures Ltd | Wholesale & retail | 2025 |
| Oseblu Ltd | Health & social care | 2026 |
| Oshafiq Ventures Ltd | Professional & scientific | 2025 |
| Osnovia Ltd | Construction | 2025 |
| OSO Partners Limited | Arts & recreation | 2026 |
| Osombest Ltd | Wholesale & retail | 2020 |
| Osprey Enterprises Limited | Wholesale & retail | 2024 |
| OSR Retail Logistics Limited | Transport & logistics | 2013 |
| OSR Warehousing Limited | Transport & logistics | 2013 |
| Osso Traders Ltd | Wholesale & retail | 2025 |
| Osun Enterprise Ltd | Real estate | 2026 |
| OT Consult CIC | Education | 2024 |
| OT Eastern Groceries Ltd | Wholesale & retail | 2025 |
| Otampi Music Ltd | Arts & recreation | 2025 |
| OTC1 Ltd | Construction | 2023 |
| OUR Dignity | Water & waste | 2021 |
| Ourpad Limited | Health & social care | 2008 |
| Outfitted Studio Ltd | Information & communication | 2026 |
| Outlook Real Estate Ltd | Households | 2026 |
| Outreach Community CIC | Health & social care | 2023 |
| Outreach Homes Ltd | Administrative & support | 2020 |
| Outtanaija Ltd | Wholesale & retail | 2024 |
| Oval Care Services UK Ltd | Administrative & support | 2016 |
| Oven Xperts Ltd | Administrative & support | 2024 |
| OVI Install Ltd | Construction | 2022 |
| Ovidiu ION Ltd | Construction | 2022 |
| Oviland Constructions Ltd | Construction | 2014 |
| OWA Properties Solutions Ltd | Real estate | 2024 |
| Oware Services Ltd | Transport & logistics | 2024 |
| OWO Socialite Club (UK) | Other services | 2023 |
| Owtt Group Ltd | Administrative & support | 2023 |
| OWU Heritage UK Ltd | Other services | 2023 |
| Oxlade Accountants Limited | Professional & scientific | 2026 |
| Oxlade Business Training School Limited | Education | 2015 |
| Oxlane Food Centre Limited | Wholesale & retail | 2020 |
| Oxload Ltd | Water & waste | 2026 |
| Oxlow Butchers Limited | Wholesale & retail | 2023 |
| Oxlow Contracts Ltd | Professional & scientific | 2025 |
| Oxlow Lane Spice Ltd | Hospitality | 2025 |
| Oxlow Ltd | Real estate | 2021 |
| Oxlow Services Ltd | Energy | 2023 |
| Oxlowdrycleaner Ltd | Other services | 2025 |
| Oxosofts PVT Ltd | Wholesale & retail | 2023 |
| Oyenson Newera International Ltd | Real estate | 2022 |
| OYO Land Management (Dagenham) Limited | Real estate | 2006 |
| OZ Security Services Ltd | Administrative & support | 2025 |
| Ozen&Co Services Ltd | Construction | 2023 |
| Ozylin Ltd | Health & social care | 2023 |
| Ozzy Healthcare Ltd | Administrative & support | 2020 |
| Ozzy Industries Ltd | Information & communication | 2026 |
| P & a London Limited | Construction | 2015 |
| P & LG Ltd | Wholesale & retail | 2011 |
| P Best Service Ltd | Construction | 2020 |
| P Construction Ltd | Construction | 2020 |
| P R Canary Building Services Limited | Energy | 2014 |
| P&A Consultants Ltd | Information & communication | 2022 |
| P&A Interiors Ltd | Construction | 2019 |
| P&G Building Solutions Ltd | Construction | 2022 |
| P&M Solution Ltd | Administrative & support | 2024 |
| P&N Brothers Ltd | Construction | 2024 |
| P&O Paving Ltd | Administrative & support | 2026 |
| P. M. J Properties Ltd | Real estate | 2025 |
| P. Smart Limited | Manufacturing | 2003 |
| P.N.C Electrical Limited | Construction | 2005 |
| Pabznvan Ltd | Transport & logistics | 2025 |
| Pace Express Ltd | Transport & logistics | 2020 |
| Pacecross Ltd | Information & communication | 2016 |
| Pacs Communication Limited | Wholesale & retail | 2011 |
| Padina Limited | Households | 2025 |
| Padmaja Textile (UK) Ltd | Wholesale & retail | 2024 |