| Lucabe Transport Ltd | Transport & logistics | 2025 |
| Lucky Jools Ltd | Information & communication | 2024 |
| Luckycoin Films Ltd | Professional & scientific | 2011 |
| Luna Digital Media Ltd | Administrative & support | 2017 |
| Lunch LAB Ltd | Hospitality | 2021 |
| Lunn Hospitality Ltd | Hospitality | 2015 |
| Lury Restaurant Ltd | Hospitality | 2024 |
| Lustro Cleaning Services Ltd | Administrative & support | 2025 |
| LUX Commercial Ltd | Construction | 2024 |
| LUX Fencing Ltd | Construction | 2024 |
| LUX Scape Group Holdings Limited | Financial services | 2024 |
| Luxco Limited | Construction | 2024 |
| Luxma Ltd | Wholesale & retail | 2024 |
| LXL Consultancy Services Limited | Professional & scientific | 2016 |
| LXL LLP | | 2009 |
| M & G Decorators Limited | Construction | 2003 |
| M & H Catering Tulleys Farm Ltd | Hospitality | 2021 |
| M & P Properties (Commercial) Limited | Real estate | 2016 |
| M & P Properties (Residential) Limited | Real estate | 2016 |
| M & Z Hasting Pizza Limited | Hospitality | 2024 |
| M Cubed Associates Ltd | Real estate | 2021 |
| M J Lamb Limited | Construction | 2012 |
| M N M Bros Ltd | Hospitality | 2021 |
| M T Commercial Fishing Limited | Agriculture & fishing | 2020 |
| M Welch Electrical Limited | Construction | 2014 |
| M&L Premium Services Ltd | Administrative & support | 2026 |
| M'S Bread Ltd | Education | 2019 |
| M. Phillips (Builders) Limited | Construction | 2008 |
| M.A. Russell & Co. (2000) Ltd. | Professional & scientific | 2005 |
| M.J.G Autos Limited | Wholesale & retail | 2015 |
| MAC N Cheese Shack Limited | Hospitality | 2022 |
| Mackways Enterprise Ltd | Wholesale & retail | 2021 |
| MAD Dash Cleaning Services Ltd | Administrative & support | 2024 |
| MAD4MOBILES (Bexhill) Limited | Wholesale & retail | 2015 |
| MAD4MOBILES2 Limited | Wholesale & retail | 2025 |
| Maddayler Ltd | Real estate | 2025 |
| Madeaux Limited | Wholesale & retail | 2011 |
| Madephoyou Ltd | Hospitality | 2025 |
| Magdalena Harmala VS Limited | Professional & scientific | 2013 |
| Magnesia MK Ltd | Wholesale & retail | 2025 |
| Magnolia Advisers Ltd | Financial services | 2025 |
| Magnus Power Limited | Manufacturing | 2019 |
| Majesco Transport Ltd | Transport & logistics | 2019 |
| Maku UK Limited | Wholesale & retail | 2014 |
| Malabis Business Ltd | Wholesale & retail | 2025 |
| Malcolm Peth (ST Leonards-On-Sea) Limited | Extraterritorial | 2004 |
| Malope Limited | Households | 2019 |
| Maltbys Property Management Limited | Real estate | 2019 |
| Mane Enterprises & Services Ltd | Real estate | 2025 |
| Mango Collective Limited | Information & communication | 2024 |
| Maple Property Limited | Real estate | 2026 |
| Marbex Limited | Construction | 2008 |
| Marc Dorfman Consulting Ltd | Professional & scientific | 2015 |
| Marcer Wealth Limited | Financial services | 2017 |
| Marchmont Asset Management Limited | Financial services | 2021 |
| Marcus Jones Developments Limited | Real estate | 2003 |
| Mardan Court (2000) Limited | Real estate | 1999 |
| Mare Films Ltd | Information & communication | 2023 |
| Margaret Sheehy Limited | Arts & recreation | 2005 |
| Margem (RYE) Limited | Administrative & support | 2007 |
| Marianne North Centre Hastings Ltd | Agriculture & fishing | 2024 |
| Marianne North HQ CIC | Arts & recreation | 2026 |
| Marianne Park Limited | Households | 1998 |
| Marina Cafe (Camber) Limited | Hospitality | 2008 |
| Mariusbusinessac Ltd | Wholesale & retail | 2020 |
| Mark MP Tranding Limited | Wholesale & retail | 2025 |
| Mark Trade Limited | Real estate | 2020 |
| Markwick Court Residents Company Limited | Households | 2000 |
| Markwick Residents' Company Limited | Households | 1997 |
| Martison Limited | Real estate | 2022 |
| Masnad Limited | Administrative & support | 2020 |
| Massive DRY Lining & Plastering Ltd | Construction | 2017 |
| Mastolf and Mastej Ltd | Wholesale & retail | 2024 |
| Matcine Limited | Information & communication | 2001 |
| Matthew Collins Financial Planning Ltd | Financial services | 2017 |
| Matyus Properties Ltd | Real estate | 2021 |
| MAX Hosting Ltd | Information & communication | 2024 |
| MAX Oliver Lewes Limited | Other services | 2020 |
| Maxima Equestrian Limited | Wholesale & retail | 2008 |
| Maxoliver Academy Brighton Ltd | Other services | 2024 |
| Maxoliver in Tunbridge Wells Limited | Other services | 2017 |
| Maxoliver Men’S Hair Limited | Other services | 2022 |
| Maxwell CBA Property Ltd | Real estate | 2019 |
| MAY DA Silva Ltd | Arts & recreation | 2026 |
| Mayka Ltd | Manufacturing | 2026 |
| MB Hastings Limited | Wholesale & retail | 2023 |
| Mccormick Building Services Limited | Construction | 1985 |
| Mcgregor Estate Planning Limited | Professional & scientific | 2024 |
| MCO 1066 Limited | Construction | 2018 |
| Mdaw Properties Ltd | Real estate | 2020 |
| Media Travel Ltd | Other services | 1992 |
| Medica Group Limited | Professional & scientific | 2013 |
| Medica IT Services Limited | Information & communication | 2020 |
| Medica Reporting Limited | Health & social care | 2004 |
| Medium Maze Limited | Information & communication | 2016 |
| Memory Tree Films Ltd | Information & communication | 2025 |
| Mental Health Help Sussex CIC | Health & social care | 2021 |
| Men’S Room Hastings & ST Leonards CIC | Health & social care | 2024 |
| Merchants (ST Leonards) Limited | Wholesale & retail | 2011 |
| Merivale Chowns Limited | Households | 1996 |