| Keep Calm VA Support Limited | Administrative & support | 2025 |
| Kempthorne House and Grounds RTM Company Ltd | Households | 2024 |
| Kent House (Management) Limited | Households | 2006 |
| Khalil's Kitchen Ltd | Wholesale & retail | 2025 |
| Kicks Martial Arts and Boxing Centre Limited | Arts & recreation | 2026 |
| King & Mcgaw Holdings Limited | Professional & scientific | 1999 |
| King & Mcgaw Limited | Manufacturing | 1999 |
| Kitchens Bathrooms NO Problems Ltd | Construction | 2025 |
| KO Cleaning Solutions Ltd | Administrative & support | 2021 |
| Kpbn Solutions Limited | Construction | 2025 |
| Kpls Legal Consultants Limited | Professional & scientific | 2022 |
| Kumyol Estates Limited | Real estate | 2018 |
| L'Isola Buona Ltd | Wholesale & retail | 2009 |
| LA Baguette Shop Limited | Hospitality | 1993 |
| Lawford Services (London) Limited | Administrative & support | 2013 |
| Lawrence Barnes Ltd | Construction | 2007 |
| LBS Buildings & Lettings Ltd | Real estate | 2023 |
| Leaflet Marketing Ltd | Professional & scientific | 2024 |
| Leforte Property Maintenance Limited | Construction | 2006 |
| Leon Estate Homes Ltd | Real estate | 2022 |
| Leon Fire Protection Ltd | Construction | 2023 |
| Less Obvious Ltd | Professional & scientific | 2009 |
| Lewes District Citizens Advice Bureau | Information & communication | 1997 |
| Lewes Training Centre Ltd | Education | 2018 |
| LH Locum Cover Ltd | Professional & scientific | 2018 |
| LID Contracting Ltd | Construction | 2016 |
| Lincolns Kitchens and Granite Limited | Manufacturing | 2014 |
| LLR Property Services Ltd | Construction | 2023 |
| Lmfp Limited | Health & social care | 2019 |
| Lotka Limited | Financial services | 2018 |
| Lotus Families | Health & social care | 2005 |
| LS Auto Parts Ltd | Wholesale & retail | 2026 |
| Ludis Design Ltd | Information & communication | 2014 |
| Ludis Publishing Group Limited | Information & communication | 2017 |
| Lukmar Ltd | Construction | 2026 |
| Luna BEA Bride Ltd | Professional & scientific | 2020 |
| M Moore Group Limited | Administrative & support | 2022 |
| M. J. Saxby Limited | Wholesale & retail | 2006 |
| Made by Finch Ltd | Professional & scientific | 2018 |
| Mamoosh Ltd | Manufacturing | 2019 |
| Mamoosh Wharf Limited | Wholesale & retail | 2024 |
| Managed Fire Solutions Ltd | Extraterritorial | 2017 |
| Manganaro Ltd | Information & communication | 2018 |
| Maple Handling + Logistics Ltd | Transport & logistics | 2000 |
| Marc Fish Limited | Manufacturing | 2014 |
| Marine Court Maintenance Limited | Households | 1990 |
| Marque Sussex Ltd | Wholesale & retail | 2020 |
| Martello Taxis Limited | Transport & logistics | 2003 |
| Mason Clay Psychological Services Ltd | Administrative & support | 2024 |
| Mayfair Court (Eastbourne) Limited | Households | 2002 |
| Meats&More Ltd | Wholesale & retail | 2023 |
| Mechanics on TAP Ltd | Wholesale & retail | 2025 |
| Medipower Limited | Water & waste | 2017 |
| Meeching Estate Agents Ltd | Real estate | 2015 |
| Meeching Place (Block 2) RTM Company Limited | Households | 2022 |
| Menteath & Co Ltd | Manufacturing | 2020 |
| Merrilees House Limited | Professional & scientific | 1997 |
| Metal Box Technology Solutions Limited | Manufacturing | 1981 |
| Mindbody Mastery Ltd | Administrative & support | 2018 |
| Mittens Investments Ltd | Construction | 2019 |
| MJB Chef Services Ltd | Hospitality | 2026 |
| MNG Power Solutions Ltd | Construction | 2025 |
| Moat Croft Court (Residents Association) Limited | Households | 1969 |
| Moda Energy Ltd | Professional & scientific | 2008 |
| Moore & Co Construction Limited | Construction | 2017 |
| Move-It Solutions Ltd | Information & communication | 2025 |
| Moyade Property Investments Ltd | Real estate | 2025 |
| MR Cycles Limited | Wholesale & retail | 2007 |
| Muddles Green Limited | Manufacturing | 2020 |
| Munger Capital Ltd | Financial services | 2018 |
| Munsley Limited | Financial services | 2020 |
| Muscle Peach Ltd | Wholesale & retail | 2024 |
| Musical Money Limited | Wholesale & retail | 2010 |
| N & G Building Services Limited | Construction | 2003 |
| Nanet Websites Ltd | Information & communication | 2020 |
| NCW Marine LLP | | 2013 |
| New Africa Trading Limited | Wholesale & retail | 2015 |
| New Horizon Properties (Rentals UK) Ltd | Real estate | 2024 |
| New Reach PR Ltd | Professional & scientific | 2021 |
| Newhaven Art Projects CIC | Education | 2025 |
| Newhaven Autocentre Ltd | Wholesale & retail | 2022 |
| Newhaven Barbers Ltd | Other services | 2024 |
| Newhaven Cafe Ltd | Hospitality | 2022 |
| Newhaven Car Services (Sussex) Ltd | Wholesale & retail | 2021 |
| Newhaven Chamber Ltd | Real estate | 2014 |
| Newhaven Fishing CIC | Manufacturing | 2023 |
| Newhaven Port & Properties Limited | Transport & logistics | 1985 |
| Newhaven Scuba Training Ltd | Arts & recreation | 2018 |
| Newleaf Camper Conversions Limited | Manufacturing | 2021 |
| Newtimber Land Management Ltd | Agriculture & fishing | 2018 |
| Nexum Power Ltd | Professional & scientific | 2025 |
| Nicholson Plant Ltd | Administrative & support | 2022 |
| Nineteen Seventy Five Management Limited | Households | 1975 |
| Northcourt House RTM Company Limited | Households | 2019 |
| Northdown Court (Newhaven) Limited | Real estate | 2023 |
| Nose Systems Limited | Information & communication | 2009 |
| Nursted Limited | Manufacturing | 2020 |
| OLA Kowalska Coaching Ltd | Education | 2020 |
| Oliver Perrott Photography Ltd | Professional & scientific | 2017 |
| Olliver Services Limited | Construction | 2016 |