| Mastercut London Limited | Manufacturing | 2019 |
| Masterkey Investment Limited | Real estate | 2026 |
| Masterpiece Makers Ltd | Extraterritorial | 2025 |
| Masters Building and Engineering Services Ltd | Construction | 2024 |
| Masters Food UK Ltd | Wholesale & retail | 2023 |
| Masters Solicitors Ltd | Professional & scientific | 2026 |
| Mastertec Limited | Wholesale & retail | 2004 |
| Masumin Limited | Health & social care | 1998 |
| MAT Consulting Limited | Wholesale & retail | 2014 |
| Mather Court Limited | Real estate | 2004 |
| Mathews & Yousaf Property Maintenance Ltd | Construction | 2025 |
| Mathews Property Investments Ltd | Real estate | 2023 |
| Mathews Property Management Ltd | Real estate | 2021 |
| Maths Momentum Ltd | Education | 2019 |
| Mathus Limited | Administrative & support | 2014 |
| Mati Express Ltd | Transport & logistics | 2025 |
| Matison Construct Ltd | Construction | 2019 |
| Matongera Limited | Information & communication | 2015 |
| Matoydel Ltd | Construction | 2021 |
| Matrion Solutions Ltd | Information & communication | 2025 |
| Matrixtax Ltd | Information & communication | 2024 |
| Matt Luff Racing Ltd | Arts & recreation | 2018 |
| Matthew Ashimolowo Media Ministries Limited | Wholesale & retail | 1998 |
| Mattu Brothers Ltd | Health & social care | 2015 |
| Mattu Construction Essex Ltd | Construction | 2020 |
| Matty Cuts Education Ltd | Education | 2025 |
| Matty Cuts Ltd | Other services | 2023 |
| Matured Leadership Consult Limited | Administrative & support | 2021 |
| Maugo Capital Investment Limited | Real estate | 2026 |
| Maugret Social Work Services Ltd | Health & social care | 2023 |
| Maury Property Ltd | Real estate | 2025 |
| MAV Foods Limited | Manufacturing | 2021 |
| Mava Group Ltd | Construction | 2023 |
| Mavco FM Group Ltd | Administrative & support | 2025 |
| Mavco Group Ltd | Administrative & support | 2024 |
| Mavco Services Ltd | Administrative & support | 2023 |
| Maverick Education Consultants Ltd | Education | 2023 |
| Mawiuk Ltd | Information & communication | 2026 |
| Mawney Accountancy Limited | Professional & scientific | 2016 |
| Mawney Limited | Professional & scientific | 2019 |
| Mawney Property Investments Limited | Real estate | 2023 |
| Mawneys Accountants Ltd | Professional & scientific | 2025 |
| Mawneys Key Ltd | Real estate | 2026 |
| Mawuena Hair Ltd | Wholesale & retail | 2024 |
| MAX B Shop Limited | Wholesale & retail | 2023 |
| MAX Grow Limited | Wholesale & retail | 2021 |
| MAX Training Centre Limited | Education | 2018 |
| Max's Caribbean Kitchen Limited | Hospitality | 2017 |
| Maxcare Consultants Limited | Health & social care | 2023 |
| Maxclean Services Limited | Administrative & support | 2024 |
| Maxfield Investments Ltd | Real estate | 2004 |
| Maxim Foods Ltd | Wholesale & retail | 2018 |
| Maximise Technology (UK) Ltd | Information & communication | 2013 |
| Maximize Enterprise Ltd | Construction | 2020 |
| Maxitech UK Limited | Professional & scientific | 2025 |
| Maxload Limited | Administrative & support | 1999 |
| Maxxloft Ltd | Construction | 2020 |
| MAY and Grace Home Ltd | Wholesale & retail | 2026 |
| May's Consultancy Services Ltd | Professional & scientific | 2023 |
| Maya's Beauty & Nails Ltd | Other services | 2017 |
| MAYA22 Group Limited | Construction | 2020 |
| Mayce Consultancy Limited | Construction | 2021 |
| Mayfair Cabs Limited | Transport & logistics | 2023 |
| Mayfair House Associates Ltd | Real estate | 2013 |
| Mayflower Gaming Ltd | Arts & recreation | 2019 |
| Mayhem Abridge Limited | Professional & scientific | 2004 |
| Mayhem London Limited | Arts & recreation | 2004 |
| Maylands Farmhouse Ltd | Hospitality | 2025 |
| Maymaxe Capital Ltd | Financial services | 2025 |
| MAZ E7 Foods Ltd | Hospitality | 2020 |
| MAZ Fashions Ltd. | Wholesale & retail | 2013 |
| MAZ Foods London Ltd | Hospitality | 2020 |
| MAZ Foods Ltd | Hospitality | 2019 |
| MAZ UK Property Ltd | Real estate | 2025 |
| Maza Capital Limited | Real estate | 2023 |
| Mazahmi Events Ltd | Hospitality | 2024 |
| Maze Box Ltd | Hospitality | 2025 |
| Mazeon (UK) Ltd | Health & social care | 2013 |
| Mazhar Investments Holding Ltd | Real estate | 2020 |
| Mazrreku Ltd | Construction | 2023 |
| Mazrreku Property UK Ltd | Real estate | 2025 |
| Mazur Team Ltd | Construction | 2020 |
| MB Cladding Ltd | Construction | 2022 |
| MB Davall Ltd | Households | 2024 |
| MB Davall Property Ltd | Households | 2024 |
| MB Fast Foods Ltd | Hospitality | 2018 |
| MB Mini Coaches Ltd | Transport & logistics | 2022 |
| MB Outdoor Living Spaces Ltd | Construction | 2021 |
| MBA Haulage Limited | Transport & logistics | 2015 |
| MBA Lettings Ltd | Real estate | 2022 |
| Mbam Consultancy Ltd | Construction | 2019 |
| Mbangug Ltd | Extraterritorial | 2024 |
| MBC Creative Limited | Information & communication | 2025 |
| MBE Fine Art Shipping Ltd | Administrative & support | 2016 |
| Mbfs Services Ltd | Construction | 2021 |
| Mbhandal Ltd | Real estate | 2025 |
| Mbhealthylife UK Ltd | Arts & recreation | 2021 |
| MBM Electrical Services Ltd | Construction | 2016 |
| MBM Electrical Solutions Ltd | Construction | 2025 |
| MBM Property Solutions Ltd | Construction | 2025 |