| Multi Homes Ltd | Construction | 2026 |
| Multi-Mix IT Limited | Information & communication | 2015 |
| Multiprofessional Surgical Services LLP | | 2026 |
| Murhaf Car Wash Ltd | Wholesale & retail | 2024 |
| Music Box Wealden CIC | Arts & recreation | 2022 |
| Music Product Limited | Information & communication | 2022 |
| MW Logistics Limited | Transport & logistics | 2021 |
| MWH Commercials Ltd | Transport & logistics | 2018 |
| Mxvi Limited | Wholesale & retail | 2025 |
| My Barista Pro Limited | Wholesale & retail | 2023 |
| My First Word Grows UP Ltd | Health & social care | 2015 |
| My Hair Wardrobe Limited | Wholesale & retail | 2025 |
| My Mortgage Company Limited | Financial services | 2015 |
| Mylan Signature Collection Ltd | Professional & scientific | 2025 |
| Nancy Khawam Family Mediation and Consultancy Ltd | Other services | 2019 |
| Nano Batch Brewing Co Ltd | Manufacturing | 2025 |
| Nantahala Medical Limited | Health & social care | 2022 |
| Nash Street Holdings Limited | Real estate | 2001 |
| Navillus Limited | Professional & scientific | 2006 |
| NB Construction (South East) Ltd | Construction | 2011 |
| Ndokin Limited | Information & communication | 2023 |
| NDR Systems Limited | Information & communication | 2008 |
| Neat Security Limited | Administrative & support | 2013 |
| Neighbourhood Agency Ltd | Professional & scientific | 2021 |
| Nenor Limited | Information & communication | 2003 |
| Neonova Ltd | Professional & scientific | 1996 |
| Neptune Design Centre Hailsham Limited | Wholesale & retail | 2010 |
| Neptune PCS Ltd | Wholesale & retail | 2024 |
| New ERA Training Facilities Limited | Financial services | 2026 |
| New ERA Training London Ltd | Arts & recreation | 2023 |
| New Motion Records Limited | Information & communication | 2010 |
| Newhaw Launderette Limited | Other services | 2004 |
| Newton & Frost Holdings Ltd | Financial services | 2017 |
| Newtspubs Ltd | Hospitality | 2019 |
| Next Line AI Limited | Administrative & support | 2025 |
| NFF Trade & Retail Ltd | Administrative & support | 2017 |
| NGB Design Limited | Professional & scientific | 2024 |
| Nical Installations Limited | Construction | 2008 |
| Nicant Ltd | Real estate | 2021 |
| Niche Jobs Limited | Administrative & support | 2008 |
| Nicholas Norman Potter Limited | Administrative & support | 2024 |
| Nick Ring Tennis & Golf Limited | Administrative & support | 2004 |
| Nick the Butcher Limited | Wholesale & retail | 2019 |
| Nightingale House Design and Build Ltd | Construction | 2022 |
| Nightingale Place Limited | Real estate | 2008 |
| Nima Print and Design Services Limited | Manufacturing | 2002 |
| NINETY10 Limited | Professional & scientific | 2018 |
| Ninfield Homes LLP | | 2022 |
| Ninfield Properties Limited | Financial services | 2022 |
| NJ Live Limited | Administrative & support | 2003 |
| NJ Roberts Associates LLP | | 2020 |
| Njroberts Consulting Ltd | Professional & scientific | 2011 |
| NK Detailing Ltd | Administrative & support | 2026 |
| NM International Ltd | Health & social care | 2016 |
| NMH Plant Hire Repairs & Maintenance Limited | Manufacturing | 2024 |
| NO 2 Garfield Road Residents Association Limited | Households | 1995 |
| NO More Robots Ltd | Information & communication | 2017 |
| NOC Consultants LLP | | 2023 |
| Norman Development Ltd | Construction | 2022 |
| North Care Home Limited | Extraterritorial | 2008 |
| North Chailey Development Limited | Construction | 2024 |
| North Crescent (Hailsham) Management Limited | Households | 2003 |
| North Cross Developments Ltd | Real estate | 2025 |
| North East Gynaecology Ltd | Health & social care | 2026 |
| North Foreland Investments Limited | Financial services | 2024 |
| North Tier Limited | Construction | 2023 |
| Northshore Shipyard Limited | Manufacturing | 2023 |
| Northshore Supermarine Limited | Professional & scientific | 2001 |
| Norwood Editorial Services Limited | Information & communication | 2026 |
| Notarify LLP | | 2024 |
| Novex Care LLP | | 2025 |
| NOW It's Personal Ltd | Wholesale & retail | 2023 |
| NOW Partners UK Limited | Professional & scientific | 2026 |
| NRW Properties Limited | Real estate | 2011 |
| NSK Precision Engineering Limited | Professional & scientific | 2002 |
| NSP Group Limited | Financial services | 2020 |
| Nstw Limited | Other services | 2007 |
| NTB Outdoors Limited | Wholesale & retail | 2018 |
| NUA Clinics Limited | Health & social care | 2025 |
| Number 151 Proprietors Limited | Households | 1971 |
| Nunningham Farm Holiday Lets Ltd | Hospitality | 2020 |
| Nutra Plumbing & Heating Limited | Construction | 2007 |
| Nutribrand Ltd | Wholesale & retail | 2017 |
| O'Connor Anaesthetics Ltd | Health & social care | 2019 |
| O'Keeffe and Partners Limited | Wholesale & retail | 2025 |
| O'Keeffe Company Ltd | Hospitality | 2025 |
| Oak Aesthetics Clinic Limited | Other services | 2025 |
| Oak and Sycamore Limited | Wholesale & retail | 2024 |
| Oakdale 19 LLP | | 2019 |
| Oakfield Farm HOG Roast & Catering Ltd | Hospitality | 2018 |
| Oakfields (Hailsham) Management Company Limited | Real estate | 2017 |
| Oakmead Investments Limited | Real estate | 2020 |
| Oakspire Developments Limited | Construction | 2025 |
| OB Carpentry and Building Services Ltd | Construction | 2026 |
| OBI WAN Properties Ltd | Real estate | 2021 |
| Obsidian Equities Ltd | Financial services | 2025 |
| Ocean Source Ltd | Wholesale & retail | 2023 |
| Ocellus Radiology LLP | | 2025 |
| Odds and Cogs Limited | Construction | 2003 |
| OFF the Wall Drinks Limited | Manufacturing | 2023 |