| Mill Carpentry & Joinery Limited | Construction | 2016 |
| Mill Hill Specsavers Hearcare Limited | Wholesale & retail | 2026 |
| Mill Hill Specsavers Limited | Wholesale & retail | 2023 |
| Millar Homes Limited | Real estate | 2025 |
| Millar Property Holdings Limited | Real estate | 2026 |
| Millennia Insights Ltd | Administrative & support | 2017 |
| Millennium Structured Networks Limited | Construction | 1999 |
| Miller Foods Limited | Hospitality | 2019 |
| Miller Vending Ltd | Construction | 2025 |
| Millers Quay Limited | Real estate | 1991 |
| Millie’S Trusted Tails Ltd | Other services | 2026 |
| Millionaires Golf Club Ltd | Wholesale & retail | 2026 |
| Millstream Pilates Ltd | Arts & recreation | 2023 |
| Millthorpe Limited | Real estate | 2011 |
| Milman Contracts Ltd | Construction | 2025 |
| Milngavie Specsavers Limited | Wholesale & retail | 2008 |
| Milngavie Visionplus Limited | Wholesale & retail | 2008 |
| Milo Sounds Limited | Arts & recreation | 2022 |
| Milton Keynes Specsavers Hearcare Limited | Wholesale & retail | 2006 |
| Milton Keynes Specsavers Limited | Wholesale & retail | 2000 |
| Milton Keynes Visionplus Limited | Wholesale & retail | 2000 |
| Mimi & Marble Tech Limited | Information & communication | 2024 |
| Mimtec Group Limited | Financial services | 2025 |
| Mimtec Limited | Manufacturing | 2006 |
| Mindcell Sales Training Ltd | Other services | 2012 |
| Mindspace Therapy Ltd | Other services | 2022 |
| Mindwater Ltd | Wholesale & retail | 2002 |
| Minehead Specsavers Limited | Wholesale & retail | 2009 |
| Mingle Connections Ltd | Professional & scientific | 2018 |
| Minhaj Property Group Ltd | Real estate | 2026 |
| Miniature Hobbies Ltd | Wholesale & retail | 2021 |
| Minimal Effective Method Limited | Arts & recreation | 2026 |
| Minimum Energy Efficiency Service Ltd | Professional & scientific | 2021 |
| Mint Holdco UK Limited | Financial services | 2019 |
| Miracle Detail Ltd | Wholesale & retail | 2022 |
| Miss Automotive Ltd | Wholesale & retail | 2023 |
| Miss Charlotte Tuition Ltd | Education | 2026 |
| Miss S - Accounting for Purpose C.I.C. | Professional & scientific | 2014 |
| Mission Prestige Limited | Wholesale & retail | 2017 |
| Mitchell Parker White Limited | Extraterritorial | 2008 |
| Mixed Method Media Ltd | Information & communication | 2014 |
| Miyabi London Ltd | Wholesale & retail | 2022 |
| MJ Abela Ltd | Professional & scientific | 2015 |
| MJ Event Hire Ltd | Administrative & support | 2025 |
| MJB Contracts Ltd | Professional & scientific | 2008 |
| Mjfree Electrical Ltd | Construction | 2014 |
| Mjnova UK Ltd | Information & communication | 2021 |
| MJR Real Estate Limited | Real estate | 1998 |
| MJS Consulting Services Limited | Professional & scientific | 2020 |
| MK Bros Investments Ltd | Real estate | 2025 |
| MK Bros Properties Ltd | Real estate | 2021 |
| MK GAS Limited | Wholesale & retail | 2006 |
| MKC Cleaning Solutions Ltd | Administrative & support | 2021 |
| MKD Electrical & Mechanical Services Ltd | Construction | 2023 |
| MKG Building Services Ltd | Construction | 2016 |
| MKG Property Investments Ltd | Real estate | 2019 |
| MKW Resources Limited | Administrative & support | 2018 |
| ML Hydrographics Ltd | Professional & scientific | 2018 |
| MLC Management Ltd | Administrative & support | 2025 |
| MLD Operations LP | | 2023 |
| MM Mobile Welding Ltd | Manufacturing | 2019 |
| MM Professional Services Limited | Wholesale & retail | 2025 |
| MMC Pharm(A) Limited | Health & social care | 2024 |
| MMD Holdings Limited | Construction | 2018 |
| MMM Couriers Ltd | Transport & logistics | 2022 |
| MMT Overseas Investment Ltd | Wholesale & retail | 2026 |
| MN Electrical Services Ltd | Construction | 2006 |
| MN House Developments Ltd | Real estate | 2024 |
| Moat Court RTM Company Limited | Households | 2018 |
| Mobility Audio Vision ENT. Ltd | Wholesale & retail | 2023 |
| Modern British Kitchens Limited | Manufacturing | 2016 |
| Modern Living Developments (General Partner) 2 Limited | Real estate | 2022 |
| Modern Living Developments (General Partner) Limited | Real estate | 2020 |
| Modo Restaurant Ltd | Hospitality | 2026 |
| Mods 4 Rolling Stock Limited | Manufacturing | 2024 |
| Modus Talent Ltd | Administrative & support | 2025 |
| Mold Specsavers Limited | Wholesale & retail | 2002 |
| Momentum Llsj Ltd | Professional & scientific | 2025 |
| Momentum Systems Limited | Information & communication | 2018 |
| Momentum TT Ltd | Professional & scientific | 2025 |
| Monarc Roofing Ltd | Construction | 2026 |
| Moneyfield Mews Management Company Limited | Real estate | 2022 |
| Monks Hill Management Company Limited | Households | 2025 |
| Monks Rest Limited | Hospitality | 2022 |
| Monks Way Flats Management Company Limited | Hospitality | 1983 |
| Monmouth Specsavers Limited | Wholesale & retail | 1990 |
| Monmouth Visionplus Limited | Wholesale & retail | 1993 |
| Mono Motorcycles 2017 Ltd | Wholesale & retail | 2023 |
| Monster Card Merchants Ltd | Wholesale & retail | 2024 |
| Monster Marine and Property Ltd | Professional & scientific | 2013 |
| Montley Ltd | Real estate | 2023 |
| Montrose Specsavers Limited | Wholesale & retail | 2002 |
| Montserrat Events & Festivals Limited | Administrative & support | 2025 |
| Monty Shipping Services Limited | Transport & logistics | 2014 |
| Monument Architecture and Design Limited | Professional & scientific | 2012 |
| Mooi Hair Extensions Ltd | Administrative & support | 2018 |
| Moonbeam Childminding Limited | Health & social care | 2021 |
| Moonflower Forest Ltd | Other services | 2025 |
| Moonstones Limited | Wholesale & retail | 2005 |
| Moor Construction Limited | Construction | 1995 |