| Middlesex Interior Division Ltd | Construction | 2011 |
| Middlesex Limited | Construction | 2005 |
| Middlesex Plastering & Drylining Limited | Extraterritorial | 2011 |
| Midway Quay (Freehold) Limited | Extraterritorial | 2009 |
| Mike Britton Design Ltd | Other services | 2015 |
| Milk, NO Sugar - Coffee Consultancy Ltd | Professional & scientific | 2017 |
| Mill Court Property Limited | Real estate | 2009 |
| Mill Park Management Company Ltd | Households | 2003 |
| Mills Bidco Limited | Financial services | 2019 |
| Mills Midco Limited | Financial services | 2019 |
| Mills Topco Limited | Financial services | 2019 |
| Millstone Management Limited | Households | 2017 |
| Mindenhurst (Brunswick Road) Management Company Limited | Households | 2018 |
| Mindful Branding Ltd | Professional & scientific | 2025 |
| Mindyasa Limited | Professional & scientific | 2019 |
| Mintec Limited | Information & communication | 1987 |
| Miracle Ventures Ltd | Administrative & support | 2015 |
| Mirror Pool Fisheries Limited | Agriculture & fishing | 2000 |
| MJ Property Partners Ltd | Households | 2025 |
| Mmmj Properties Ltd | Real estate | 2022 |
| Modular Vehicle Systems Ltd | Wholesale & retail | 2023 |
| Module Solutions Limited | Information & communication | 2003 |
| Molly Millars Management Company Limited | Households | 2011 |
| Mooli Consulting Ltd | Wholesale & retail | 2024 |
| Moorcroft Freehold Limited | Real estate | 2018 |
| Moore Trimmings Ltd | Administrative & support | 1996 |
| Moorfields (NED Lane, Bradford) Management Company Limited | Households | 1998 |
| Moreganic Limited | Hospitality | 2021 |
| Moretvicar Limited | Administrative & support | 2010 |
| Motion Orthopaedics Limited | Extraterritorial | 2007 |
| Movie Vehicle Specialists Ltd | Real estate | 2017 |
| MPC (Holdings) Limited | Construction | 2019 |
| MPS1 Consulting Ltd | Information & communication | 2021 |
| MPS1 Investment Holdings Ltd | Financial services | 2023 |
| MR Van MAN Bucks Ltd | Construction | 2023 |
| Mrdalekjd Ltd | Information & communication | 2013 |
| Msgthatreg UK Ltd | Information & communication | 2024 |
| Mtlp Care Limited | Health & social care | 2022 |
| Mulberry Court (East Bierley) Limited | Households | 2003 |
| Muna Esco Ltd | Construction | 2024 |
| Muna Group Ltd | Professional & scientific | 2024 |
| Muna Ventures Ltd | Wholesale & retail | 2024 |
| MV SFX Limited | Information & communication | 2019 |
| MX Core Ltd | Construction | 2024 |
| My Childrens Therapy Ltd | Health & social care | 2023 |
| MYP Properties Limited | Real estate | 2018 |
| N Compass UK Limited | Administrative & support | 2004 |
| N M Cabling Limited | Administrative & support | 2001 |
| Namah Investments Ltd | Financial services | 2020 |
| Naomifeldstudio Limited | Professional & scientific | 2025 |
| Natural Scenes Ltd | Information & communication | 2005 |
| Naylor Accountancy Services (Bourne END) Limited | Professional & scientific | 2003 |
| NBW Project Management and Construction Ltd | Construction | 2025 |
| Neil Baker Associates Ltd | Other services | 2011 |
| Next Jeneration Developments Ltd | Real estate | 2025 |
| Next Level Business Group Limited | Professional & scientific | 2015 |
| NGA Estates Ltd | Financial services | 2024 |
| Nicholls Close Management Company Limited | Households | 2005 |
| NIP IT in the BUD Ltd | Administrative & support | 2024 |
| NO Pattern Limited | Information & communication | 2023 |
| Nolu's Nuts Ltd | Manufacturing | 2023 |
| North Road (Woking) Management Limited | Households | 2003 |
| Northmead (Slough) Management Association Limited | Households | 1981 |
| Northrange Capital Ltd | Construction | 2017 |
| Nowa Amani Vault Club Ltd | Financial services | 2025 |
| Nsmg Group Ltd | Financial services | 2026 |
| Nsmg Strategic Advisory Ltd | Information & communication | 2026 |
| Nuainsight Ltd | Professional & scientific | 2020 |
| Nyme Properties LLP | | 2015 |
| Oaklands Management Company (NO. 1) Limited | Households | 2007 |
| OCL Carpentry (UK) Limited | Construction | 2006 |
| Odiham Road (Riseley) Management Company Limited | Households | 2019 |
| OFF Duty Foods Ltd | Manufacturing | 2026 |
| OG Motors Limited | Wholesale & retail | 2025 |
| Oichef Ltd | Hospitality | 2020 |
| Old Farm Court Residents Association Limited | Households | 1999 |
| Old Kiln Road (Management Company) Limited | Households | 2024 |
| Old Pump House (Bishopsworth Road ) Management Company Limited | Households | 2020 |
| Oliver Gordon Limited | Professional & scientific | 2019 |
| One Altea Limited | Administrative & support | 2014 |
| One High Street (Egham) Management Company Limited | Households | 2018 |
| Opal X Limited | Manufacturing | 2012 |
| Openmatter Limited | Administrative & support | 2006 |
| Oracle Snooker Clubs Limited | Real estate | 1991 |
| Orange Grove Designs Ltd | Information & communication | 2014 |
| Orchard Grange NO.2 (Wokingham) Management Company Limited | Households | 2017 |
| Orchid Investments Limited | Construction | 2019 |
| Original Kicks Ltd | Wholesale & retail | 2023 |
| Orleigh Cross Management Company (Newton Abbot) Limited | Extraterritorial | 2008 |
| Osborne Mews (Clevedon) Management Company Limited | Households | 2004 |
| Oscars CNC Ltd | Construction | 2023 |
| Otter Place Residents Management Company Limited | Households | 2012 |
| OTV Birwelco Limited | Financial services | 1989 |
| Outsource ME Estimating Ltd | Administrative & support | 2017 |
| OXYGEN8 Consulting Limited | Professional & scientific | 2018 |
| P J Boyd Marketing Limited | Professional & scientific | 2016 |
| Paintworx Bourne END Limited | Wholesale & retail | 2016 |
| PAN & Tilt Productions Limited | Information & communication | 2003 |
| Pancho & Kable Ltd | Wholesale & retail | 2019 |
| Paneuro Windows Ltd | Administrative & support | 2013 |