| MIH Capital Limited | Information & communication | 2026 |
| Mija Ltd | Health & social care | 2019 |
| Mike Allgrove Planning Limited | Professional & scientific | 2019 |
| Mike Best Consultants Limited | Transport & logistics | 2006 |
| Mike KUS Limited | Information & communication | 2011 |
| Milathan Limited | Information & communication | 2012 |
| Miles and Clark Limited | Information & communication | 2019 |
| Miles for Minds Ltd | Arts & recreation | 2026 |
| Miles-Ip Ltd | Financial services | 2025 |
| Milestone Management (Chichester) Limited | Real estate | 2014 |
| Milford Aviation Services Limited | Transport & logistics | 2004 |
| Mill Close (Fishbourne) Flat Owners Residents Association Limited | Households | 1970 |
| Mill Farm Plants Limited | Agriculture & fishing | 2021 |
| Mill Wall Securities Limited | Real estate | 1967 |
| Millbourn Ross Limited | Professional & scientific | 2020 |
| Millennium Bridge Capital (Research) Ltd | Information & communication | 2025 |
| Millis Potter Travel Ltd | Administrative & support | 2016 |
| Millpond Electrical Ltd | Construction | 2026 |
| Millstone Landscapes Limited | Other services | 1993 |
| Millwood Emsworth Management Company Limited | Households | 2025 |
| Milow Properties Ltd | Real estate | 2012 |
| Mini Mops Limited | Administrative & support | 2013 |
| Minster Bridal Chichester Ltd | Wholesale & retail | 2020 |
| Mintex Ltd | Wholesale & retail | 2013 |
| Miray Cafe Ltd | Hospitality | 2018 |
| Misha & Co Design Studio Ltd | Professional & scientific | 2025 |
| Miso Essex Limited | Hospitality | 2024 |
| Misom Limited | Financial services | 2020 |
| Miss Angela Skull Limited | Health & social care | 2024 |
| Miss SEE Ltd | Wholesale & retail | 2019 |
| Misty Shell Ltd | Health & social care | 2005 |
| MIT Barbers Ltd | Other services | 2026 |
| Mitchell Travel Ltd | Administrative & support | 2022 |
| Miwaste Ltd | Water & waste | 2025 |
| MJ & TF Lacy Partnership Limited | Hospitality | 2003 |
| MJ Commercial Cleaning Limited | Administrative & support | 2013 |
| MJ Visual Limited | Extraterritorial | 2007 |
| MJA Electrics Limited | Construction | 2025 |
| MJB (Partnership) Limited | Financial services | 1998 |
| MJL 77 Ltd | Arts & recreation | 2019 |
| MJM Care Group Ltd | Health & social care | 2024 |
| Mjms Group Ltd | Other services | 2025 |
| MJN Tractors Limited | Wholesale & retail | 2017 |
| Mjpaediatrics Ltd | Health & social care | 2022 |
| MKB Joinery Limited | Construction | 2015 |
| MKW Property Enterprises Ltd | Extraterritorial | 2025 |
| MLH Detailing & Valeting Ltd | Other services | 2023 |
| MM Cleaner Service Ltd | Administrative & support | 2025 |
| Mmhb Management Communal Area Limited | Administrative & support | 2015 |
| Mmhb Management Limited | Construction | 2003 |
| Mmholdingsuk Ltd | Professional & scientific | 2023 |
| MMI Sussex Ltd | Construction | 2016 |
| MNR Coaching Ltd | Administrative & support | 2013 |
| Mobi Publishing Ltd | Information & communication | 2011 |
| Modern Classics Hairdressing Limited | Other services | 2015 |
| Modern Marketplace Ltd | Wholesale & retail | 2025 |
| Moldovan Ltd | Construction | 2020 |
| Mole Investments Limited | Financial services | 2022 |
| Momentum Journeys Ltd | Education | 2023 |
| Monexapps Ltd | Information & communication | 2025 |
| MONITOR365 Ltd | Information & communication | 2021 |
| Monkeychimp Consultancy Ltd | Health & social care | 2018 |
| Monohome UK Ltd | Wholesale & retail | 2020 |
| Monro Management Ltd | Real estate | 2024 |
| Montanna House Ltd | Administrative & support | 2019 |
| Montclair House RTM Company Limited | Households | 2026 |
| Moore (South) R&I LLP | | 2016 |
| Moore B Limited | Wholesale & retail | 2026 |
| Moore Home Spaces Ltd | Hospitality | 2020 |
| MOR Flooring Limited | Wholesale & retail | 2019 |
| More Brains Cooperative Ltd | Other services | 2020 |
| More Distance Golf Ltd | Wholesale & retail | 2023 |
| More East Yoga Limited | Administrative & support | 2025 |
| More Than Just Figures Limited | Professional & scientific | 2022 |
| More Than Windows Limited | Construction | 2011 |
| Morelli Consulting Ltd | Professional & scientific | 2011 |
| Morgan Capital Investments Ltd | Real estate | 2019 |
| Morgans Walk Properties Limited | Real estate | 2016 |
| Morley & Sons Roofing Ltd | Construction | 2019 |
| Morley Funfairs Ltd | Arts & recreation | 2020 |
| Mortice & Tenon Bespoke Furniture Limited | Manufacturing | 2014 |
| Mortlock and Sons Limited | Construction | 2002 |
| Mosse Futures Ltd | Arts & recreation | 2021 |
| Mosse New Holdings Ltd | Financial services | 2022 |
| Mossy Earth Ltd | Agriculture & fishing | 2017 |
| MOT Connect Ltd | Professional & scientific | 2024 |
| Mother’S of Pearl Group Ltd | Public administration | 2022 |
| Motion Automotive Ltd | Wholesale & retail | 2012 |
| Motion Building Services Limited | Construction | 2019 |
| Motion Drive Films Ltd | Information & communication | 2025 |
| Motor Claims Network Limited | Administrative & support | 2011 |
| Motor NET Ltd | Real estate | 1998 |
| Motor-Tech Vehicle Repairs Ltd | Wholesale & retail | 2023 |
| Motorforce (Chichester) Limited | Wholesale & retail | 2006 |
| Motte & Bailey Cafe Limited | Hospitality | 2024 |
| Mount Pleasant Eastergate Ltd | Financial services | 2018 |
| Mouseclix Limited | Administrative & support | 2018 |
| Moyler & SON Ltd | Real estate | 2013 |
| Mpag Properties Limited | Real estate | 2011 |
| MPM2 Limited | Professional & scientific | 2002 |