| NZ Aesthetics and Beauty Ltd | Other services | 2024 |
| NZA Investments Limited | Real estate | 2026 |
| NZK9 Ltd | Administrative & support | 2026 |
| NZO Properties Limited | Real estate | 2023 |
| NZO Solutions Limited | Information & communication | 2019 |
| O & O Construction Ltd | Construction | 2019 |
| O & U Services Limited | Hospitality | 2022 |
| O Aroriode Limited | Construction | 2018 |
| O R Real Estate Limited | Real estate | 2025 |
| O&N Contracts Ltd | Construction | 2023 |
| O'Maya Flowers Limited | Wholesale & retail | 2025 |
| O-Opera Limited | Administrative & support | 2026 |
| O.Bartholomew Ltd | Construction | 2024 |
| Oabt Ltd | Wholesale & retail | 2025 |
| OAJ Healthcare Ltd | Health & social care | 2025 |
| Oak & Door Ltd | Administrative & support | 2026 |
| Oak Enterprise & Investments Ltd | Construction | 2023 |
| Oak Fort Ltd | Financial services | 2023 |
| Oak Gardens Property Ltd | Real estate | 2015 |
| Oak House Childrens Home Ltd | Health & social care | 2013 |
| Oak House Lettings Ltd | Real estate | 2023 |
| Oak Lodge Care Essex Ltd | Health & social care | 2026 |
| Oak Property Services Limited | Real estate | 2024 |
| Oak Security Services Limited | Administrative & support | 2015 |
| Oak Tree London Ltd | Real estate | 2021 |
| Oakdan Carpentry Ltd | Manufacturing | 2026 |
| Oakglade Catering Limited | | 1982 |
| Oakland Estate Investment Ltd | Real estate | 2017 |
| Oakland Maintenance Ltd | Construction | 2017 |
| Oakland Real Estates Ltd | Households | 2024 |
| Oakland Residential Services Ltd | Households | 2024 |
| Oakland Ventures Ltd | Real estate | 2026 |
| Oaklands Estates Ltd | Real estate | 2006 |
| Oaklead Limited | Other services | 2021 |
| Oakley Cleaning Limited | Administrative & support | 2020 |
| Oakline Property Limited | Households | 2025 |
| Oaklodge Property Limited | Real estate | 2020 |
| Oaklodge Supporting Living Limited | Health & social care | 2014 |
| Oakmere Limited | Real estate | 2026 |
| Oakmont Homes (NO.10) Ltd | Real estate | 2022 |
| Oakmont Homes (NO.11) Ltd | Real estate | 2023 |
| Oakmont Homes (NO.3) Ltd | Construction | 2015 |
| Oakmont Homes (NO.4) Ltd | Construction | 2016 |
| Oakmont Homes (NO.5) Ltd | Construction | 2016 |
| Oakmont Homes (NO.8) Ltd | Real estate | 2017 |
| Oakmont Homes (NO.9) Ltd | Real estate | 2018 |
| Oakmont Homes Construction Ltd | Other services | 2015 |
| Oakmont Homes Group Ltd | Other services | 2015 |
| Oakmont Homes Ltd | Real estate | 2016 |
| Oakside PIE Mash & Cafe Ltd | Hospitality | 2025 |
| Oakstone Trading Ltd | Other services | 2025 |
| Oaktree Financials Ltd | Professional & scientific | 2017 |
| Oakwood Gate Limited | Real estate | 2024 |
| Oakwright Services Ltd | Construction | 2026 |
| Oan&Dan Delivery Ltd | Transport & logistics | 2022 |
| Oasis Banqueting Services Limited | Hospitality | 2015 |
| Oasis Club Properties Limited | Professional & scientific | 1995 |
| Oasis Global Investments Limited | Financial services | 2022 |
| Oasis Homes and Estates Ltd | Real estate | 2022 |
| Oasis International Limited | Professional & scientific | 2020 |
| Oasis Places Limited | Health & social care | 2005 |
| Oasis Property Developer Limited | Real estate | 2015 |
| Oasis Property Investments Ltd | Real estate | 2021 |
| Obakem Care Ltd | Health & social care | 2025 |
| Obbs Ltd | Wholesale & retail | 2014 |
| OBC Essex Ltd | Other services | 2023 |
| Obfuscora Ltd | Information & communication | 2025 |
| Objectverse Technologies Ltd | Information & communication | 2022 |
| OBM Onelab CIC | Public administration | 2018 |
| Obsgynae Ltd | Health & social care | 2014 |
| Obsidiantime Ltd | Wholesale & retail | 2026 |
| Obunda International Ltd | Information & communication | 2023 |
| OC & Associates Limited | Financial services | 2013 |
| Occasionz Party Hire Ltd | Hospitality | 2020 |
| Occasionz Whippy Ltd | Hospitality | 2026 |
| Ocean 2023 Ltd | Hospitality | 2023 |
| Ocean Blue Services Ltd | Wholesale & retail | 2024 |
| Ocean Business Management Ltd | Real estate | 2021 |
| Ocean Business Services Ltd | Professional & scientific | 2019 |
| Ocean Design London Ltd | Manufacturing | 2021 |
| Ocean Properties Investment Limited | Construction | 2026 |
| Oceanic Property Investment Ltd | Construction | 2020 |
| Oceanport Limited | Transport & logistics | 2019 |
| OCJ Electrical Ltd | Construction | 2018 |
| OCP Investments Limited | Real estate | 2020 |
| Octa Accountants Ltd | Professional & scientific | 2022 |
| Octa Clinical Group Ltd | Wholesale & retail | 2022 |
| Octa Retail Limited | Wholesale & retail | 2025 |
| Octa Studios Ltd | Professional & scientific | 2025 |
| Octagon PUB Company Ltd | Hospitality | 2017 |
| Octo Cars Ltd | Transport & logistics | 2024 |
| October Developments Ltd | Construction | 2019 |
| Octokhan Investment Services Ltd | Professional & scientific | 2004 |
| Octopus Media International Limited | Information & communication | 2015 |
| Octosoft Limited | Information & communication | 2018 |
| ODI Foods Ltd | Hospitality | 2025 |
| Odin's V Ltd | Wholesale & retail | 2021 |
| OF ALL Things Ltd | Arts & recreation | 2022 |
| Offered Impex Limited | Wholesale & retail | 2025 |
| Office of Hair Ltd | Wholesale & retail | 2024 |