| Morriss Properties Limited | Real estate | 2024 |
| Morrisson Carpentry Limited | Construction | 2026 |
| Mortgage Brands Holding Limited | Financial services | 2025 |
| Mortgage Integrity Limited | Financial services | 2024 |
| Mortimer and Spake Engineering Limited | Professional & scientific | 2003 |
| Mortivation Limited | Arts & recreation | 2018 |
| Morton Pattison Ltd | Administrative & support | 2015 |
| Morts Plumbing & Heating Limited | Construction | 2017 |
| Moseley Enterprises Limited | Professional & scientific | 2002 |
| Mosnek Int'L Ltd | Health & social care | 2021 |
| Moss Monkey Limited | Information & communication | 2024 |
| Mostlane Construction Limited | Construction | 2017 |
| Mostlane Facilities Management Limited | Construction | 2021 |
| Mostlane Group Limited | Construction | 2021 |
| Mostlane Holdings (Southern) Limited | Professional & scientific | 2009 |
| Mother Homeopathy Limited | Health & social care | 2026 |
| Motherlandcuisine Ltd | Wholesale & retail | 2025 |
| Motion Charters Limited | Other services | 2013 |
| Motion Marine UK Limited | Manufacturing | 2023 |
| Motion Robotics Limited | Professional & scientific | 2013 |
| MOTIV8 for Life C.I.C. | Education | 2013 |
| Motive Marine (Southern) Limited | Manufacturing | 2014 |
| Motive Marine UK Ltd | Manufacturing | 2019 |
| Motocolor (Southampton) Limited | Wholesale & retail | 2003 |
| Motocolor Limited | Extraterritorial | 1983 |
| Motoexpress Limited | Wholesale & retail | 2019 |
| Motomatic Limited | Wholesale & retail | 2025 |
| Motorbike Parts Limited | Wholesale & retail | 2018 |
| Motorhome Marketplace (South) Ltd | Wholesale & retail | 2022 |
| Motorhouse SRC Limited | Wholesale & retail | 2005 |
| Motorsium Ltd | Administrative & support | 2023 |
| Motorvait Limited | Professional & scientific | 2021 |
| Motorworld Car Bodyshop Ltd | Wholesale & retail | 2003 |
| Motovation Global Limited | Administrative & support | 2022 |
| Mots (Southampton) Limited | Extraterritorial | 2024 |
| Mottisfont Capital LP Ltd | Other services | 2018 |
| Mottisfont Limited | Professional & scientific | 2011 |
| Mottisfont Management Ltd | Professional & scientific | 2013 |
| Mottisfont Verussol UK Ltd. | Manufacturing | 2016 |
| Mottram Midco Limited | Financial services | 2021 |
| Mottram Nominees Limited | Professional & scientific | 2024 |
| Mottram Pictures Limited | Information & communication | 2023 |
| Mottram Topco Limited | Financial services | 2021 |
| Motus Executive Personnel Ltd | Professional & scientific | 2024 |
| MOU Consulting Limited | Wholesale & retail | 2020 |
| Moula Enterprise Ltd | Hospitality | 2019 |
| Mouland Electrical Ltd | Construction | 2023 |
| Moulsdale Carpentry Limited | Manufacturing | 2019 |
| Mount Construction Services Limited | Construction | 2017 |
| Mount Hythe Residents Association Limited(The) | Other services | 1965 |
| Mount Vinson Limited | Real estate | 2023 |
| Mountain Trans Ltd | Transport & logistics | 2024 |
| Mountainhigh Limited | Hospitality | 1981 |
| Mountaintop Services Limited | Professional & scientific | 2018 |
| Mountbatten Education & Training Consultancy Ltd | Education | 2023 |
| Mountbatten Hampshire Limited | Administrative & support | 2008 |
| Mountbatten Hampshire Promotions Ltd | Administrative & support | 1998 |
| Mountford Estates Limited | Real estate | 1994 |
| Mountrest Limited | Health & social care | 2014 |
| Mountview Residents Company Limited | Households | 1995 |
| Moura's Restaurant Limited | Hospitality | 2024 |
| Moutasim Medical Ltd | Health & social care | 2019 |
| Move 2 IT Limited | Administrative & support | 2016 |
| Move in Letting Agents Limited | Real estate | 2018 |
| Moving and Storage Limited | Professional & scientific | 2014 |
| Mowbary Limited | Real estate | 1998 |
| Mowill Group Ltd | Health & social care | 2013 |
| Moxham Extraction Ltd | Construction | 2023 |
| Moyo Energy Limited | Professional & scientific | 2009 |
| MOZ Morris Ltd | Information & communication | 2014 |
| Mozenty Ltd | Transport & logistics | 2019 |
| Mozumder Enterprise Ltd | Hospitality | 2023 |
| Mo’S Removals Ltd | Transport & logistics | 2025 |
| MP Auto Garages Limited | Wholesale & retail | 2025 |
| MP Cars Specialists Ltd | Wholesale & retail | 2025 |
| MP Digital Services Ltd | Information & communication | 2023 |
| MP Landscaping and Brickwork Ltd | Administrative & support | 2024 |
| MP Lettings and Property Management Limited | Real estate | 2025 |
| MP Tyres Ltd | Wholesale & retail | 2024 |
| MP Venture Limited | Wholesale & retail | 2010 |
| Mp&Sons Environmental Ltd | Water & waste | 2021 |
| MPC Global Business Venture Limited | Information & communication | 2011 |
| MPH South Ltd | Construction | 2026 |
| Mpjk Ltd | Real estate | 2023 |
| MPK Plumbing & GAS Services Limited | Construction | 2016 |
| MPL Law Limited | Professional & scientific | 2020 |
| MPQ Properties Limited | Real estate | 2016 |
| MPR Resourcing Services Ltd | Administrative & support | 2019 |
| MPS Group Holdings Ltd | Wholesale & retail | 2023 |
| Mpwb Consultancy Ltd | Other services | 2025 |
| MPY Accountancy Services Ltd | Professional & scientific | 2018 |
| Mqfocus Limited | Information & communication | 2000 |
| MR Celee Limited | Wholesale & retail | 2025 |
| MR Chase Building Company Limited | Construction | 2015 |
| MR Cloud Limited | Information & communication | 2017 |
| MR FLO Heating & Plumbing Limited | Other services | 2015 |
| MR H Carpets & Flooring Limited | Wholesale & retail | 2015 |
| MR HE Take Away Ltd | Hospitality | 2016 |
| MR Justin Bishop Ltd | Professional & scientific | 2025 |
| MR LCD Limited | Wholesale & retail | 2007 |