| M Lamputt Limited | Households | 2019 |
| M M OST Ltd | Health & social care | 2011 |
| M Patil Ltd | Health & social care | 2014 |
| M Press Consultancy Ltd | Professional & scientific | 2025 |
| M S L Property Limited | Real estate | 2000 |
| M Scape Ltd | Professional & scientific | 2010 |
| M Ventures Ltd | Professional & scientific | 2024 |
| M&A Treading Limited | Construction | 2024 |
| M&M Luxury Limited | Financial services | 2019 |
| M&N Painting & Decorations Ltd | Construction | 2025 |
| M&P Kitchens Ltd | Construction | 2014 |
| M&P Scaffold Limited | Construction | 2025 |
| M. & C. Holdings (Bath) Limited | Professional & scientific | 1972 |
| M. C. Hughes Consulting Limited | Professional & scientific | 2005 |
| M. J. Cawley Consulting Ltd | Information & communication | 2020 |
| M. R. Fellingham Limited | Professional & scientific | 2025 |
| M.Morant Ltd | Professional & scientific | 2024 |
| M.S DMD Ltd | Health & social care | 2023 |
| M2 Investment Partners Ltd | Financial services | 2018 |
| M2AF Ltd | Professional & scientific | 2026 |
| M2H2 LLP | | 2017 |
| M4 Autos Ltd | Administrative & support | 2026 |
| M4 Property Management Ltd | Real estate | 2018 |
| MA Innovative Ltd | Wholesale & retail | 2020 |
| MA SAN Auction Ltd | Administrative & support | 2016 |
| Mabel Bear Ltd | Real estate | 2025 |
| MAC Communications Ltd | Information & communication | 2017 |
| MAC37 Limited | Hospitality | 2019 |
| Macabre Tours UK Ltd | Administrative & support | 2025 |
| Macabseil Limited | Administrative & support | 2025 |
| Macgregor Smith (Holdings) Limited | Financial services | 2017 |
| Macgregor-Smith Limited | Professional & scientific | 2002 |
| Mach 2 Consulting Ltd | Professional & scientific | 2023 |
| Machine Investments Ltd | Information & communication | 2022 |
| Mackay Consulting Services Ltd | Professional & scientific | 2024 |
| Macreedy Limited | Professional & scientific | 2011 |
| MAD MAX Tours Ltd | Administrative & support | 2007 |
| MAD Media Services Ltd | Information & communication | 2020 |
| Mad-Rad Reporting Ltd | Professional & scientific | 2016 |
| Madaxe Ltd | Information & communication | 2022 |
| Made in the UK Ltd | Wholesale & retail | 2010 |
| Made IT MA Limited | Real estate | 2019 |
| Made With Limited | Information & communication | 2016 |
| MAG TV Limited | Information & communication | 2012 |
| Magara PI Ltd | Construction | 2026 |
| Magdalen Avenue (Management) Limited | Households | 1983 |
| Magee’S Bees Ltd | Wholesale & retail | 2022 |
| Magenta AI Limited | Information & communication | 2023 |
| Magic Consulting House Ltd | Professional & scientific | 2024 |
| MAGIC4 Ltd | Health & social care | 2022 |
| Magical Music and Movement Limited | Administrative & support | 2012 |
| Magid Scissors Barber Bath Ltd | Other services | 2020 |
| Magma Labs Ltd | Financial services | 2025 |
| Magna Manor Developments Limited | Construction | 2013 |
| Mahalakshmi Global Limited | Information & communication | 2025 |
| Mahony Cleaning Limited | Administrative & support | 2012 |
| MAI Thai Limited | Hospitality | 2010 |
| Maidstone (Somerset) Ltd | Construction | 2025 |
| Maikai Group Limited | Arts & recreation | 2020 |
| Mainstay Designs Limited | Professional & scientific | 2000 |
| Maintenance END Ltd | Manufacturing | 2019 |
| Maison KA Group UK Ltd | Hospitality | 2024 |
| Maisons DE France Limited | Extraterritorial | 1983 |
| Maitrics Limited | Information & communication | 2025 |
| Majority Market Limited | Professional & scientific | 2008 |
| Mak&Na Limited | Health & social care | 2014 |
| Maka Consulting Ltd | Construction | 2025 |
| Makan Developments Limited | Real estate | 2007 |
| Make Your Figures Count Limited | Administrative & support | 2008 |
| Make Yourself at Home (Bath) Limited | Real estate | 2024 |
| Mala Developments Limited | Professional & scientific | 2015 |
| Malcolm Lippiatt (SPV) Limited | Construction | 2025 |
| Mall Impact Limited | Real estate | 2019 |
| Malmaine Limited | Real estate | 2020 |
| Malna Holdings Limited | Financial services | 2025 |
| Maltarch Limited | Professional & scientific | 1984 |
| Malthouse (Bath) Limited | Hospitality | 2017 |
| Malyn Property Company Limited | Real estate | 1965 |
| Mambo MAN Limited | Professional & scientific | 2016 |
| Maminka Ltd | Wholesale & retail | 2024 |
| MAN Friday Technology Limited | Information & communication | 2025 |
| Manage My Website LLP | | 2022 |
| Manage Your Mortgage Ltd | Professional & scientific | 2016 |
| Mandalyns Ltd | Hospitality | 2011 |
| Manera Homes Limited | Construction | 2026 |
| Mango HR Limited | Administrative & support | 2015 |
| Manipura House Ltd | Health & social care | 2025 |
| Manisa Properties Ltd | Real estate | 2025 |
| Mann Williams (Belfast) Limited | Construction | 2025 |
| Mann Williams Limited | Construction | 1998 |
| Manning Park Ltd | Hospitality | 2023 |
| Manor Castle Properties Limited | Real estate | 2002 |
| Manor Study Tours Limited | Administrative & support | 2000 |
| Manor Villas (Bath) Management Company Limited | Households | 2012 |
| Manroproperty Ltd | Real estate | 2016 |
| Mansi Ltd | Professional & scientific | 2010 |
| Mantaray (Bath) Ltd | Construction | 2002 |
| Manton Holdings Limited | Real estate | 2017 |
| Maple Music Limited | Information & communication | 2001 |
| Maple Stadward Ltd | Professional & scientific | 2002 |