| JNA Group Ltd | Information & communication | 2022 |
| John Rhodes Autospeed Ltd. | Wholesale & retail | 2013 |
| JON RAY Consultancy Limited | Professional & scientific | 2003 |
| Jonathan Godfrey Garden Maintenance Ltd | Administrative & support | 2024 |
| Jott Enterprises Ltd | Information & communication | 2025 |
| Jscw Holdings Limited | Administrative & support | 2024 |
| Jscw Properties Limited | Wholesale & retail | 2021 |
| JT Computer Solutions Limited | Information & communication | 2005 |
| Jubilant Limited | Information & communication | 2007 |
| Jump Start Productions Ltd | Information & communication | 2009 |
| Juno Consulting Limited | Professional & scientific | 2026 |
| Just Candles Limited | Wholesale & retail | 2013 |
| Just Chilli'N JAM Ltd | Hospitality | 2024 |
| Just Live-In Care Ltd | Public administration | 2020 |
| Kams Solutions Ltd | Wholesale & retail | 2025 |
| Kedale Construction Limited | Construction | 2017 |
| Kent Classic Spares Limited | Wholesale & retail | 1997 |
| Kent Holdings Group Ltd | Other services | 2022 |
| Kid-Ethic Ltd | Professional & scientific | 2013 |
| Killingworth Estates Limited | Real estate | 2011 |
| Kings Court Management (Eastbourne) Limited | Households | 1991 |
| Kings Court Residents Company (Eastbourne) Limited | Households | 2007 |
| Kingsfold Court Management Limited | Households | 1991 |
| KLM (Brighton) Properties Limited | Real estate | 2019 |
| Koolearth Group Investments Limited | Real estate | 2020 |
| Kronaxis Limited | Construction | 2023 |
| Kutter Ltd | Manufacturing | 2026 |
| L & P Commercials Ltd | Real estate | 2015 |
| LA Squadra Ltd | Hospitality | 2021 |
| Lancaster Property Holdings Ltd | Construction | 2021 |
| Landfine Limited | Financial services | 2019 |
| Landmark Paving Company Limited | Construction | 2008 |
| Lanes Eatery Ltd | Hospitality | 2024 |
| Lanes Seaford Ltd | Hospitality | 2022 |
| Langrich Limited | Administrative & support | 2025 |
| LB Retail Ltd | Wholesale & retail | 2019 |
| LEE Hudson Lift Services Ltd | Manufacturing | 2003 |
| Lending & Technology Consultancy Limited | Professional & scientific | 2022 |
| Lenham Motor Company Limited | Wholesale & retail | 1987 |
| Lewes Station Book Shop Limited | Wholesale & retail | 2009 |
| Lewes Swim School Limited | Education | 2022 |
| Lewisaustinhomes Ltd | Real estate | 2019 |
| Lexden Court Residential 2000 Limited | Households | 2000 |
| Life Church Seaford | Other services | 2020 |
| Lime Building (Services) Limited | Wholesale & retail | 2014 |
| Lime Exteriors Limited | Administrative & support | 2018 |
| Lime Landscapes Limited | Professional & scientific | 2012 |
| Lincoln Court Peacehaven RTM Company Limited | Households | 2016 |
| Lisa PEA Limited | Administrative & support | 2020 |
| Little Blue Dinosaur Media Ltd | Information & communication | 2023 |
| LJ Property Ltd | Real estate | 2019 |
| Lochin Marine International Limited | Extraterritorial | 2024 |
| Lois Brewer Photography Ltd | Information & communication | 2023 |
| London Commercial Offerings Limited | Real estate | 2025 |
| Lsea Consultancy Ltd | Professional & scientific | 2019 |
| Lucky DK Ltd | Transport & logistics | 2024 |
| Ludis Marketing Consulting Ltd | Information & communication | 2023 |
| Lummera Consulting Ltd | Administrative & support | 2013 |
| Lunatique UN Limited | Professional & scientific | 2013 |
| Lunobi Ltd | Professional & scientific | 2018 |
| M Hughes Electrical Limited | Construction | 2015 |
| M&M Accountancy and Bookkeeping Services Limited | Professional & scientific | 2023 |
| MAD About Tax Limited | Professional & scientific | 2013 |
| Madeira Way Flat Management Limited | Households | 2004 |
| Madeira Way RTM Company Limited | Households | 2007 |
| Magda Harbour Limited | Health & social care | 2023 |
| Magic Flute Investment Management Ltd | Administrative & support | 2024 |
| MAID2HELP Limited | Administrative & support | 2015 |
| Manor Court (Sutton Avenue, Seaford) Limited | Other services | 1988 |
| Mansi-Burnett Residence Ltd | Real estate | 2024 |
| Marcos Heritage Limited | Wholesale & retail | 2009 |
| Margaret Court (Peacehaven) RTM Company Limited | Households | 2019 |
| Marine Court (Seaford) Management Limited | Households | 1971 |
| Mark Cousins Limited | Construction | 2002 |
| Mark Pigram Ltd | Extraterritorial | 2024 |
| Marsino Clothings Ltd | Wholesale & retail | 2026 |
| Martello Mews Residents Limited | Households | 1999 |
| Martyn Jemison Accountancy Limited | Real estate | 2003 |
| Master the Spotlight Ltd | Education | 2023 |
| MAT Miel Transport Ltd | Transport & logistics | 2025 |
| Matt Garman Ltd | Professional & scientific | 2014 |
| Maverick Boat Adventures Limited | Administrative & support | 2022 |
| Maverick Pure Water Limited | Water & waste | 2024 |
| Mcevoy-Peall Consultancy Limited | Professional & scientific | 2021 |
| MCL Transport Consultants Ltd | Professional & scientific | 1998 |
| Mcnealys Ltd | Construction | 2025 |
| Medical English Plus Limited | Education | 2018 |
| MEG Property Holdings Limited | Financial services | 2020 |
| Mendall Auto Services Limited | Wholesale & retail | 2002 |
| Merrivale Limited | Construction | 2025 |
| Merrivale Renco Ltd | Real estate | 2026 |
| Metro AV Limited | Administrative & support | 2007 |
| MGR Consulting Ltd | Professional & scientific | 2013 |
| MH Digital Ltd | Professional & scientific | 2014 |
| Michael Upton Heating & Plumbing Ltd | Other services | 2019 |
| Michael Upton Properties Ltd | Real estate | 2025 |
| Micklefield Nursery School (Seaford) | Education | 1964 |
| Milchester House (Meads) Limited | Households | 1995 |
| Mind Nature Studio Community Interest Company | Professional & scientific | 2024 |
| Misato Auto Ltd | Wholesale & retail | 2026 |