| ME Aspect Ltd | Wholesale & retail | 2022 |
| ME Global Solutions Ltd | Administrative & support | 2026 |
| Mech.Managed Limited | Construction | 2017 |
| Mechanical Design Consultants Ltd | Professional & scientific | 2023 |
| MED WAV Limited | Transport & logistics | 2025 |
| Media Hire Limited | Administrative & support | 2018 |
| Medimarks Limited | Information & communication | 2024 |
| Medirite Limited | Wholesale & retail | 2012 |
| Medlock DRY Construction (Battersea) Limited | Construction | 2025 |
| Medlock Homes (23) Limited | Real estate | 2020 |
| Medwell Construction Limited | Construction | 2011 |
| Megacat Holdings Limited | Information & communication | 2017 |
| Mehqs Consulting Ltd | Professional & scientific | 2025 |
| Mellissa LO Ltd | Information & communication | 2016 |
| Meraki Vanlife Ltd | Manufacturing | 2021 |
| Meridian Property (U.K.) Limited | Real estate | 2015 |
| Meridian Surveyors LLP | | 2021 |
| Meridian Surveyors Sussex Limited | Extraterritorial | 2010 |
| Meridian Toilet Hire Limited | Extraterritorial | 2012 |
| Merila P Ltd | Health & social care | 2007 |
| Metal Powder and Process Limited | Manufacturing | 2013 |
| Metal Recoveries (Newhaven) Limited | Extraterritorial | 1989 |
| Metaltech Precision Engineers Ltd | Manufacturing | 2000 |
| Metrail Construction Limited | Construction | 2007 |
| Metrail Contracting Limited | Extraterritorial | 2011 |
| Metrail International Limited | Professional & scientific | 2026 |
| Metropolitan Premium Finance Limited | Financial services | 2002 |
| MEW Ventures Limited | Professional & scientific | 2020 |
| MF Plastering Limited | Construction | 2026 |
| MFC Outdoor Stores Limited | Wholesale & retail | 2011 |
| MG Carpentry Services Ltd | Manufacturing | 2026 |
| Mgear Operatives Limited | Administrative & support | 2017 |
| MGM Electrical Ltd | Construction | 2026 |
| MGW Contractors Limited | Wholesale & retail | 2008 |
| Michael O'Neill Limited | Wholesale & retail | 2012 |
| Michael Sutherland Oven Cleaning Ltd | Administrative & support | 2025 |
| Microtrends Limited | Information & communication | 2006 |
| MID Sussex Business Park (Management) Limited | Real estate | 2008 |
| Mid-Sussex Model Engineering Club Limited | Arts & recreation | 1997 |
| Midis Touch Ltd | Information & communication | 2025 |
| Mighty Bright Limited | Wholesale & retail | 2014 |
| Mill Street Properties (Maidstone) Limited | Real estate | 2003 |
| Millie's Pottery Ltd | Manufacturing | 2022 |
| Millie's Pottery-Eu Ltd | Manufacturing | 2023 |
| Milton Road Properties Limited | Real estate | 2005 |
| Mimble Ltd | Manufacturing | 2026 |
| Mini Magic Motors Ltd | Wholesale & retail | 2022 |
| Miracle Digital Entertainment Ltd | Information & communication | 2015 |
| Miracle Media Investments Ltd | Information & communication | 2015 |
| Mirox (RYE) Ltd | Real estate | 2020 |
| Mirox Holdings Ltd | Construction | 2019 |
| Mirox Homes Ltd | Construction | 2020 |
| Mirox Property (BR) Limited | Real estate | 2022 |
| Missing Link Conference Company Limited | Administrative & support | 1996 |
| Mission Laser Ltd | Arts & recreation | 2023 |
| Mister Q Consulting Limited | Wholesale & retail | 2024 |
| Mitchell & Cooper (Holdings) Limited | Professional & scientific | 2004 |
| Mitchell & Cooper Limited | Manufacturing | 1975 |
| Mitchell Heating Services Limited | Construction | 2003 |
| Mitchell's Groundscare Machinery Services Ltd | Other services | 2011 |
| Mitchell's Mowers Ltd | Wholesale & retail | 2021 |
| MJ Cars (Sussex) Limited | Wholesale & retail | 2026 |
| Mj's Cutting Edge Solutions Ltd | Construction | 2016 |
| MJB Installations Ltd | Construction | 2003 |
| MJF Electrical Contractors Ltd | Construction | 2023 |
| MJH Plumbing & Heating Limited | Construction | 2019 |
| MJS Horton Limited | Real estate | 2022 |
| MJS Media Ltd | Professional & scientific | 2015 |
| MKD Property Limited | Construction | 2014 |
| ML International Trading Company Ltd | Wholesale & retail | 2011 |
| ML Investment Properties Limited | Real estate | 2022 |
| MLC Fabrications Ltd | Manufacturing | 2024 |
| MM Private Hire Limited | Transport & logistics | 2022 |
| MM Rental Properties Limited | Real estate | 2022 |
| Mobile and Leisure Concepts Limited | Real estate | 1984 |
| Mobile Car Electrics Ltd | Professional & scientific | 2019 |
| Mobility Homestyle Limited | Construction | 2008 |
| Momai MAA Limited | Real estate | 2025 |
| Mono Communications Limited | Professional & scientific | 2025 |
| Monsoon Automotive Limited | Wholesale & retail | 1982 |
| Moon Rock Media Ltd | Information & communication | 2023 |
| Moore & Saunders Electrical Contractors Limited | Construction | 2016 |
| Moore & Saunders Holdings Limited | Financial services | 2025 |
| Moore & Saunders Investments Limited | Real estate | 2025 |
| Moore Financial Solutions Limited | Financial services | 2014 |
| Mooshka Ltd | Real estate | 2014 |
| Morris Orthopaedics Limited | Health & social care | 2023 |
| Mother Theresa's Meals Limited | Hospitality | 2006 |
| Motorbike Tours Ltd | Administrative & support | 2025 |
| MP Edits Limited | Information & communication | 2015 |
| MPD (UK Sales) Limited | Wholesale & retail | 1996 |
| MPS Trading Ltd. | Wholesale & retail | 2001 |
| MR H MOT Centre Limited | Administrative & support | 2010 |
| MR Keith Gunning Limited | Health & social care | 2019 |
| MR L.A Beauty Ltd | Wholesale & retail | 2025 |
| MR Land & Fishing Ltd | Administrative & support | 2026 |
| MSP Property Maintenance Limited | Construction | 2002 |
| MTC2 Ltd | Professional & scientific | 2009 |
| Mtechnology Group Limited | Information & communication | 2019 |
| MTH Medical Ltd | Health & social care | 2025 |