| Lottbridge Investments Ltd | Extraterritorial | 2022 |
| Lotus Retail Limited | Wholesale & retail | 2013 |
| Love Louise Ltd | Professional & scientific | 2019 |
| Love Music Travel Limited | Administrative & support | 2012 |
| LP Landscapes Limited | Administrative & support | 2009 |
| LSG (Europe) Limited | Professional & scientific | 1981 |
| LST Plant Services Ltd | Manufacturing | 2024 |
| LST Property Holdings Ltd | Real estate | 2025 |
| Luckhurst Investments Limited | Real estate | 2020 |
| Lumberscapes Ltd | Agriculture & fishing | 2025 |
| Lumenate Marketing Solutions Limited | Professional & scientific | 2024 |
| Lumina Pension Solutions Ltd | Administrative & support | 2025 |
| Luna Blue Paraplanning Ltd | Administrative & support | 2022 |
| Luna Relay Limited | Arts & recreation | 2023 |
| Luxe Auto Shine Ltd | Wholesale & retail | 2024 |
| Luxury Nails Hailsham Ltd | Other services | 2022 |
| LXK Utilities Ltd | Extraterritorial | 2024 |
| Lyell House Ltd | Health & social care | 2026 |
| Lynsey Hipgrave Limited | Information & communication | 2010 |
| Lynx Lets Limited | Real estate | 2016 |
| Lynx Property Construction Limited | Construction | 2001 |
| Lynx Property Estates Limited | Real estate | 1999 |
| Lyons Electrical & Security Ltd | Construction | 2022 |
| M & a Care Limited | Health & social care | 1995 |
| M & M Dental Laboratory Limited | Health & social care | 2019 |
| M & S Commercial Properties Limited | Real estate | 2013 |
| M & S Electrical (UK) Limited | Construction | 2002 |
| M a Enterprises Sussex Limited | Other services | 2012 |
| M Barclay Developments Ltd | Construction | 2011 |
| M C Electrical (SE) Limited | Construction | 2022 |
| M Curran Limited | Health & social care | 2024 |
| M D Stone Anaesthetic Services Limited | Health & social care | 2019 |
| M Espach Limited | Health & social care | 2019 |
| M Field & Sons Limited | Construction | 2002 |
| M J Properties (South East) Ltd | Real estate | 2020 |
| M K Baig Limited | Health & social care | 2019 |
| M Moving Management Limited | Financial services | 2021 |
| M T Property Maintenance Ltd | Construction | 2018 |
| M W Fencing and Landscaping Limited | Construction | 2018 |
| M Whitmore Landscape Garden Contractors Limited | Administrative & support | 2002 |
| M&D Healthcare Limited | Health & social care | 2010 |
| M&L Properties (Sussex) Ltd | Real estate | 2023 |
| M&S Rental Properties Limited | Real estate | 2023 |
| M. Bell Investments Ltd | Financial services | 2020 |
| M.D.J. Light Brothers (Scrap Processers) Limited | Water & waste | 1971 |
| M.K. Properties Limited | Real estate | 1972 |
| MA Property Solutions Ltd | Real estate | 2014 |
| MAC 2 Exhibitions Limited | Administrative & support | 2007 |
| Macasso Limited | Real estate | 2021 |
| Mackenzie Surgical Limited | Health & social care | 2025 |
| Made by Spoken Limited | Administrative & support | 2019 |
| Madecourt Limited | Wholesale & retail | 1998 |
| Magnolia House Services Ltd | Real estate | 1997 |
| Magpar LLP | | 2007 |
| Makdissi Holdings Limited | Financial services | 2023 |
| Makdissi Limited | Wholesale & retail | 2026 |
| Make Real Ltd | Information & communication | 2001 |
| Mallon Holdings Limited | Real estate | 2021 |
| MAN Power Solutions UK Ltd | Administrative & support | 2022 |
| Mandate Communications Group Limited | Professional & scientific | 2024 |
| Mandate Creative Limited | Professional & scientific | 2019 |
| Mann Engineering & Consultancy Limited | Professional & scientific | 2023 |
| Manna and Manna Limited | Administrative & support | 2010 |
| Manning Commercial Property Ltd | Real estate | 2024 |
| Mannings Events Limited | Arts & recreation | 2023 |
| Mannings Fairview Company Limited | Arts & recreation | 2000 |
| Manor Court (Heathfield) Management Limited | Real estate | 2003 |
| Maple (156) Limited | Households | 2001 |
| Maplewise Ltd | Professional & scientific | 2003 |
| Maplewood Drive Management Company Ltd | Households | 2017 |
| Marantech Ltd | Information & communication | 2016 |
| March Plumbing & Heating Limited | Construction | 2003 |
| Marco Properties Sussex LLP | | 2017 |
| Marco Wealth Management Limited | Administrative & support | 2020 |
| Marine View Freehold Ltd | Households | 2023 |
| Mark a S Hall Limited | Professional & scientific | 2003 |
| Mark Bloom Design Ltd | Professional & scientific | 2017 |
| Mark Gibb Structures Limited | Professional & scientific | 2013 |
| Mark Holland Wealth Management Limited | Professional & scientific | 2008 |
| Marshman Consulting Ltd | Information & communication | 2013 |
| Martin & Bowles Limited | Construction | 2012 |
| Martin & Bowles Property Maintenance Limited | Construction | 2002 |
| Martlet Education Limited | Extraterritorial | 2023 |
| Mason’S Deliver Ltd | Transport & logistics | 2019 |
| Massilia Bay Limited | Hospitality | 2022 |
| Master Properties 2022 Ltd | Real estate | 2022 |
| Mastering Life Ltd | Health & social care | 2023 |
| Matchboard Limited | Manufacturing | 1992 |
| Matisse & NHM Ltd | Information & communication | 2014 |
| Matt Williams Cardiac Imaging Limited | Health & social care | 2024 |
| MATT6 Limited | Financial services | 2026 |
| Maverick Capital Limited | Real estate | 2020 |
| MBA Networks Limited | Information & communication | 2007 |
| MC Mechanics Limited | Wholesale & retail | 2008 |
| Mcdonagh Illustration Ltd | Arts & recreation | 2026 |
| MCJ Automotive Ltd | Wholesale & retail | 2024 |
| Mcsorley Properties Ltd | Households | 2023 |
| MD Barbers Hailsham Ltd | Other services | 2025 |
| MD Practice Consultants Ltd | Health & social care | 2021 |
| MD Support Design Ltd | Professional & scientific | 2024 |