| KJM Caravan Damp Repairs Ltd | Manufacturing | 2023 |
| KLC South East Ltd | Construction | 2024 |
| KNP Consultancy Limited | Professional & scientific | 2020 |
| Koilanpur Limited | Hospitality | 2025 |
| KPS Southern Limited | Manufacturing | 1995 |
| Krystal Enterprises Europe Ltd | Transport & logistics | 2007 |
| KSD Engineering Limited | Professional & scientific | 2015 |
| KW Welding and Fabrication Ltd | Manufacturing | 2024 |
| L & L Star Inn Ltd | Hospitality | 2025 |
| L a K Electrical Ltd | Construction | 2022 |
| L C Farming Services Limited | Agriculture & fishing | 2011 |
| L-Tech Installations LLP | | 2004 |
| Lacuna Design LLP | | 2018 |
| Larraby Land Taunton Limited | Construction | 2003 |
| Lauren Barri Holstein CIC | Other services | 2025 |
| Lawrence Hammond Limited | Construction | 1997 |
| Lawyers for Nature CIC | Professional & scientific | 2020 |
| Leading 4 Life Ltd | Extraterritorial | 2019 |
| Leisure Innovation Limited | Professional & scientific | 1989 |
| Let's DO Business (South East) Group Limited | Public administration | 2010 |
| Let's DO Marketing Limited | Professional & scientific | 2023 |
| LEWES82 Ltd | Hospitality | 2026 |
| Lexado Ltd | Construction | 2008 |
| LHH Residential Property Limited | Real estate | 2018 |
| Lighten UP Sussex Ltd | Construction | 2025 |
| Lindependent Investments Limited | Real estate | 2019 |
| LIS Bauer Ltd | Health & social care | 2026 |
| Little Horse Lunges Residents Association Ltd | Households | 2020 |
| Litty Liquor Ltd | Wholesale & retail | 2022 |
| Live Fitness Limited | Arts & recreation | 2020 |
| Lodge Group Care UK Limited | Health & social care | 2007 |
| Lodge Group Holdings Limited | Financial services | 2016 |
| Lombard Plumbing Services Limited | Construction | 2006 |
| Lone Wolf Retro Ltd | Wholesale & retail | 2018 |
| Lorri Scott Creative Imaging Ltd. | Professional & scientific | 2014 |
| Louisa MAY Ltd | Hospitality | 2016 |
| Ltraffic Limited | Manufacturing | 2013 |
| Lucas Bond Limited | Wholesale & retail | 2005 |
| Luxurious Nails Ltd | Wholesale & retail | 2022 |
| Lynne Phair Consulting Ltd | Professional & scientific | 2013 |
| M & H Logging LLP | | 2020 |
| M & S Construction Sussex Limited | Construction | 2024 |
| MAC Salts Ltd | Manufacturing | 2021 |
| Making Tax Digital Assist Ltd | Professional & scientific | 2021 |
| MAN Down Ltd | Professional & scientific | 2016 |
| Maple Homes (Sussex) Ltd | Real estate | 2018 |
| Mariposa Investments | Financial services | 2019 |
| Mark Brumell Creative Services Limited | Professional & scientific | 2006 |
| Mark Jones Decorating Limited | Construction | 2002 |
| Marklake Limited | Real estate | 2016 |
| Martin Sourcing Global Ltd | Wholesale & retail | 2022 |
| Master Your Mind Limited | Other services | 2000 |
| Masterclass Developments Limited | Agriculture & fishing | 2000 |
| Matiam Holdings Ltd | Professional & scientific | 2022 |
| Matiam Ltd | Professional & scientific | 2011 |
| Mayfly Capital Limited | Real estate | 2026 |
| Maywood Construction Ltd | Construction | 2021 |
| MB Pest Control Services Ltd | Administrative & support | 2020 |
| MB Service & Repair Engineers Limited | Professional & scientific | 2014 |
| MBT Surveys Ltd | Professional & scientific | 2024 |
| MC Sourcing Services Limited | Administrative & support | 2012 |
| MD Locks Ltd | Administrative & support | 2008 |
| MD Storage Solutions Ltd | Real estate | 2016 |
| MDS Mechanical Services Ltd | Wholesale & retail | 2021 |
| Meadowbrook Design Ltd | Professional & scientific | 2021 |
| Meliora Farm CIC | Agriculture & fishing | 2026 |
| Meltech Corporation UK Ltd | Construction | 2014 |
| Mermaidlounge Ltd | Hospitality | 2025 |
| Merricks Education Limited | Education | 2024 |
| Mesbabuet Ltd | Wholesale & retail | 2025 |
| Metalium Precision Engineering Limited | Manufacturing | 2015 |
| Metrinomics UK Ltd | Professional & scientific | 2010 |
| MG Warren Solutions Limited | Administrative & support | 2021 |
| MGM Property Services Limited | Construction | 2009 |
| Mibid Limited | Administrative & support | 2025 |
| Michael Butcher Landscapes LLP | | 2016 |
| Micronet Technology Limited | Information & communication | 1996 |
| MID Devon Auctions Ltd | Wholesale & retail | 2021 |
| Mile High Paragliding Limited | Arts & recreation | 2017 |
| Mill House Farm Holdings Limited | Hospitality | 2020 |
| Milton Keynes Property Investments Limited | Real estate | 2024 |
| Minamint Ltd | Manufacturing | 2023 |
| Mindful Oak Sussex CIC | Administrative & support | 2024 |
| Mining Analyst Consulting Limited | Mining & quarrying | 2005 |
| MK Saha Venture Ltd | Real estate | 2018 |
| Mocanu Mobile Ltd | Wholesale & retail | 2016 |
| Modular Paving Group Ltd | Construction | 2019 |
| Modular Paving Limited | Construction | 2001 |
| Moerse Ideas Limited | Professional & scientific | 2023 |
| Mole Security Limited | Administrative & support | 2021 |
| Moores Gypsy Cobs Limited | Agriculture & fishing | 2021 |
| More Community Wellness CIC | Health & social care | 2026 |
| MOW & Go Sussex Ltd | Administrative & support | 2022 |
| MR and MRS G Campbell Property Ltd | Real estate | 2021 |
| Mrktfy.Com Ltd | Professional & scientific | 2025 |
| Muckypupsparlour Ltd | Other services | 2025 |
| Multipoint Property Maintenance Ltd | Construction | 2024 |
| Munrolondon Limited | Wholesale & retail | 2020 |
| Music in Mayfield Limited | Arts & recreation | 1998 |
| My Employment Ltd | Information & communication | 2018 |