| Mars Electrical Ltd | Construction | 2020 |
| Mars Outpost Limited | Wholesale & retail | 2022 |
| Mars Publication UK Limited | Administrative & support | 2019 |
| Mars Secura Advisors Limited | Professional & scientific | 2023 |
| Marsden Homes Developments & Rentals Limited | Real estate | 2025 |
| Marsh External Cleaning Limited | Administrative & support | 2025 |
| Marsh Motors Limited | Wholesale & retail | 2004 |
| Marshall AI Engineering Ltd | Information & communication | 2025 |
| Marshall Decorators Limited | Construction | 2007 |
| Marshall Development Economics Ltd | Professional & scientific | 2017 |
| Marshall FD Services Ltd | Professional & scientific | 2010 |
| Marshall Law Ltd | Administrative & support | 2024 |
| Marshall's Refrigeration Ltd | Manufacturing | 2011 |
| Marshall-Marten Limited | Professional & scientific | 2013 |
| Marshlands Animal Care Limited | Extraterritorial | 2009 |
| Marston Road Management Co Ltd | Households | 2019 |
| Martech Information Systems Limited | Professional & scientific | 1989 |
| Martha Willis Limited | Administrative & support | 2024 |
| Marthajackson Ltd | Wholesale & retail | 2015 |
| Martial Dynamo Ltd | Professional & scientific | 2026 |
| Martial Records Ltd | Information & communication | 2026 |
| Martin & Co Properties Ltd | Real estate | 2020 |
| Martin + Co Ltd | Real estate | 2023 |
| Martin and Chandon Ltd | Wholesale & retail | 2025 |
| Martin Bennett Photography Limited | Professional & scientific | 2006 |
| Martin Brewer Creative Limited | Professional & scientific | 2019 |
| Martin Chambers & Partners Limited | Real estate | 1949 |
| Martin Cody Sculpture Ltd | Arts & recreation | 2025 |
| Martin Conroy & SON Limited | Construction | 1972 |
| Martin Courier Limited | Transport & logistics | 2025 |
| Martin Dabek Photography Ltd | Professional & scientific | 2025 |
| Martin Jowett Consulting Limited | Professional & scientific | 2024 |
| Martin Motorcycle Company Ltd | Manufacturing | 2020 |
| Martin Parr & Co Limited | Professional & scientific | 2010 |
| Martin Parr Foundation | Education | 2014 |
| Martin Parr Photography LLP | | 2010 |
| Martin Properties (South West) Limited | Real estate | 2025 |
| Martin Richings Motor Repairers Limited | Wholesale & retail | 2005 |
| Martin Stowell Ltd | Construction | 2024 |
| Martineau-Farr Ltd | Hospitality | 2026 |
| Martinhal Ocean View Limited | Real estate | 2010 |
| Martino Abbattista Engineering Ltd | Professional & scientific | 2018 |
| Martlet Zero Ltd | Information & communication | 2026 |
| Martock Limited | Wholesale & retail | 2012 |
| Marton Catering Limited | Hospitality | 2025 |
| Marton Health Limited | Health & social care | 2022 |
| Martrain Limited | Professional & scientific | 2003 |
| Martyn Harries Sound Limited | Information & communication | 2009 |
| Martyn Wallbridge Financial Management Ltd | Professional & scientific | 2015 |
| Martyn Weeks Consultancy Limited | Professional & scientific | 2005 |
| Maru Art Ltd | Arts & recreation | 2025 |
| Maru Masters & Co Ltd | Extraterritorial | 2026 |
| Maru Search & Consultancy Limited | Administrative & support | 2020 |
| Maruso Ltd | Health & social care | 2016 |
| Marvell Technology UK Limited | Information & communication | 2000 |
| Marvengroup Workwear Ltd | Manufacturing | 2026 |
| Marvstan Limited | Wholesale & retail | 2026 |
| Marwah Properties Holding Limited | Construction | 2023 |
| Marwel Ltd | Extraterritorial | 2021 |
| Marwood Building Services Ltd | Construction | 2023 |
| Mary Carter Ltd | Extraterritorial | 2023 |
| Mary Celeste Limited | Extraterritorial | 2021 |
| Mary Harrison Associates Ltd | Arts & recreation | 2020 |
| Mary Homes Limited | Real estate | 2019 |
| Mary Mody Publishing Ltd | Information & communication | 2024 |
| Mary Motors Ltd | Wholesale & retail | 2024 |
| Mary Seacole Court Management Company Limited | Real estate | 2006 |
| Mary Shaw Fine Art Limited | Arts & recreation | 2014 |
| Maryam Lounge Ltd | Hospitality | 2026 |
| Marylebone Psychiatry Limited | Health & social care | 2018 |
| Maryo Gold Services Ltd | Wholesale & retail | 2020 |
| MAS Construction SW Ltd | Construction | 2019 |
| MAS Garage Services Ltd | Wholesale & retail | 2017 |
| MAS Maya UK Ltd | Wholesale & retail | 2025 |
| MAS Property Rentals Ltd | Real estate | 2021 |
| Masala HUT Bristol Ltd | Hospitality | 2020 |
| Masala Kitchen Bath Ltd | Hospitality | 2024 |
| Masala Kitchen Bristol Ltd | Hospitality | 2019 |
| Masala Master Bristol Limited | Hospitality | 2024 |
| Masala Spice Bristol Limited | Hospitality | 2019 |
| Masamo Care Limited | Health & social care | 2013 |
| Mascona Limited | Construction | 1995 |
| Mase Construction Ltd | Construction | 2012 |
| Mase Developments Limited | Real estate | 2020 |
| Masheer Consulting Ltd | Professional & scientific | 2025 |
| MASKAN786 Ltd | Real estate | 2024 |
| Maskell Engineering Services Ltd | Professional & scientific | 2025 |
| Maslen & Kiely Cheesemongers Ltd | Wholesale & retail | 2022 |
| Maso Consulting Limited | Professional & scientific | 2000 |
| Mason Court Management Company Limited | Households | 1991 |
| Mason Mobile Barber Ltd | Other services | 2025 |
| Mason Software Solutions Ltd | Information & communication | 2018 |
| Masonmovesbristol Limited | Water & waste | 2019 |
| Masons Developments SW Ltd | Construction | 2022 |
| Masp Ltd | Construction | 2025 |
| Mass Developments UK Limited | Construction | 2000 |
| Mass Interiors Limited | Wholesale & retail | 2022 |
| Mass Spec Analytical Limited | Manufacturing | 1994 |
| Masscapital Ltd | Professional & scientific | 2018 |
| Massey Cladding Solutions Limited | Construction | 2008 |