| M P Reed Ltd | Manufacturing | 2021 |
| M R Composite Ltd | Construction | 2025 |
| M R Priestley Consultancy Limited | Professional & scientific | 2017 |
| M&A Railtraining Limited | Administrative & support | 2005 |
| M&E Building Services Consultant Limited | Construction | 2023 |
| M&N Estate Services Limited | Other services | 2016 |
| M&V Service Ltd | Wholesale & retail | 2019 |
| M. K. RAJ Limited | Wholesale & retail | 2023 |
| M. Roberts Services Ltd | Manufacturing | 2026 |
| M.D. Collins and Sons Ltd | Construction | 2017 |
| M.K. Electrical Consulting Ltd | Construction | 2023 |
| M.O.J. Engineering Limited | Manufacturing | 1995 |
| M.R. Hutchins & Co. Ltd | Professional & scientific | 2008 |
| M.W.G Properties Limited | Real estate | 2017 |
| MA & G Services Ltd | Professional & scientific | 2025 |
| MA Ballet Coaching Ltd | Education | 2025 |
| Mach 1 Aviation Adjusting Ltd | Professional & scientific | 2026 |
| Machine Power Media Ltd | Information & communication | 2024 |
| Macs Decorators Ltd | Construction | 2026 |
| Mactar Co Ltd | Construction | 2023 |
| Made in Place Design Limited | Professional & scientific | 2012 |
| Made in Place Homes Limited | Administrative & support | 2014 |
| Made in Place Limited | Extraterritorial | 2009 |
| Madgex Holdings Limited | Information & communication | 2017 |
| Madgex Limited | Information & communication | 2000 |
| Madgex Two Limited | Administrative & support | 2017 |
| Madgwick Cars Limited | Manufacturing | 2001 |
| Madhu BAN East Witterings Limited | Hospitality | 2017 |
| Madushan Property Ltd | Real estate | 2025 |
| Maestro Cycling Tours Ltd | Administrative & support | 2025 |
| Maestro Racing UK 2022 Limited | Manufacturing | 2022 |
| MAG West Sussex Ltd | Hospitality | 2023 |
| Magnolia Walk Residents Limited | Households | 2018 |
| Mailtec Limited | Manufacturing | 2009 |
| Maison Tile Solutions Limited | Construction | 2020 |
| Making Theatre Gaining Skills C.I.C. | Education | 2013 |
| Malla Trade Ltd | Wholesale & retail | 2026 |
| Maltravers JAM Limited | Hospitality | 2021 |
| Manhire LLP | | 2017 |
| Manley Enterprises Limited | Wholesale & retail | 2002 |
| Manor Copse (Grove Road) Limited | Real estate | 2006 |
| Manor Court (Elmer Sands) Limited | Households | 1982 |
| Manor Electrical Limited | Construction | 1989 |
| Maple (228) Limited | Real estate | 2004 |
| Marc Wheatley Circular Distribution Limited | Administrative & support | 2010 |
| Marconi's Wireless Telegraph Company Limited | Extraterritorial | 2003 |
| Marechal Flats (Management) Limited | Households | 1970 |
| Marge & ME Ltd | Manufacturing | 2024 |
| Marine Court (Bognor Regis) Limited | Real estate | 2001 |
| Marine Fibre Composites Ltd | Professional & scientific | 2025 |
| Marine Park RTM Company Limited | Households | 2010 |
| Mario Auto Keys Ltd | Wholesale & retail | 2021 |
| Mario Paving and Landscaping Limited | Construction | 2025 |
| Mark Shepherd Acupuncture Ltd | Health & social care | 2023 |
| Market Focus Limited | Education | 2017 |
| Market Focus Properties Ltd | Real estate | 2011 |
| Markulin Ltd | Professional & scientific | 2025 |
| Marlborough House Residents Association Limited | Households | 1998 |
| Marlon Carrington Limited | Administrative & support | 2014 |
| Marsh Inns Ltd | Hospitality | 2024 |
| Marshalls Planning Services Ltd | Construction | 2025 |
| Martin Diprose Limited | Administrative & support | 2015 |
| Marventry Limited | Transport & logistics | 2026 |
| Marzany Ltd | Other services | 2025 |
| Mashnuri Ltd | Wholesale & retail | 2026 |
| Masongate Limited | Administrative & support | 1979 |
| Masters Engineering Company Limited | Professional & scientific | 2023 |
| Mastersen Ltd | Professional & scientific | 2018 |
| Matform One Limited | Administrative & support | 2008 |
| Matform Two Limited | Administrative & support | 2008 |
| Mather Air Solutions Ltd | Construction | 2024 |
| Matt Chiddle Plastering Ltd | Construction | 2017 |
| Matt O'Halloran Haulage Limited | Transport & logistics | 2020 |
| Matt Young Life Coaching Ltd | Health & social care | 2024 |
| Mattali Limited | Real estate | 2015 |
| Matters of Intimacy Ltd | Other services | 2019 |
| Matthew Harrison Flooring Limited | Construction | 2022 |
| Maverick Publishing Consultants Ltd | Professional & scientific | 2025 |
| MAW PUB Company Ltd | Hospitality | 2025 |
| Mawuedem Limited | Health & social care | 2014 |
| May's the Village Agent Limited | Real estate | 2012 |
| Mayfield Court (Pagham) Limited | Real estate | 2010 |
| Mayzak Ltd | Financial services | 2026 |
| Mazubi Orchids Ltd. | Agriculture & fishing | 2025 |
| MB Telecoms and Security Ltd | Construction | 2020 |
| Mcha Ltd | Information & communication | 2018 |
| Mcphilemy Surveying Services Ltd | Professional & scientific | 2014 |
| Mcrae Court (Selsey) Limited | Households | 2003 |
| MD 10 Ltd | Wholesale & retail | 2011 |
| Meadowside (Slinfold) Residents Management Company Limited | Households | 2021 |
| Mechanical Broadcast Engineering Limited | Professional & scientific | 2022 |
| Medi Savvy Limited | Wholesale & retail | 2024 |
| Mediglow.Co Ltd | Health & social care | 2025 |
| Meeson Limited | Wholesale & retail | 2022 |
| Mehdig Limited | Real estate | 2021 |
| Mels Engineering Ltd | Professional & scientific | 2025 |
| Meno Belly Limited | Health & social care | 2024 |
| Meranti Building and Carpentry Ltd | Construction | 2022 |
| Mercury AML Ltd | Other services | 2017 |
| Mercuryx Solutions Ltd | Professional & scientific | 2025 |