| MGE Lettings Ltd | Real estate | 2024 |
| MGH Interiors Limited | Construction | 2007 |
| MGL Window Cleaning Services Ltd | Administrative & support | 2024 |
| MGM Training Services Ltd | Other services | 2016 |
| MGR Traditional Metal Roofing Ltd. | Construction | 2020 |
| MHA Trading Ltd | Wholesale & retail | 2012 |
| Mhlh Properties Limited | Real estate | 2023 |
| MHT UK Ltd | Other services | 2014 |
| MIA Holdings Ltd | Real estate | 2019 |
| MIA Z Express Ltd | Transport & logistics | 2021 |
| Miabeth Ltd | Health & social care | 2023 |
| Miah's Fish and Chips Ltd | Hospitality | 2018 |
| Miami Supplements Portsmouth Ltd | Wholesale & retail | 2021 |
| Mica Developments Limited | Real estate | 2014 |
| Mica Properties Limited | Real estate | 2007 |
| Miceve Logistics Ltd | Hospitality | 2023 |
| Michael Mckinson Limited | Arts & recreation | 2021 |
| Michael's Decorators Limited | Construction | 2023 |
| Micky's Chips Limited | Hospitality | 2019 |
| MID Halls Ltd | Administrative & support | 2024 |
| Middlemarch Enterprises Ltd | Professional & scientific | 2022 |
| Midland First Electrical Ltd | Construction | 2023 |
| Midway Consulting Limited | Information & communication | 2025 |
| Midwinters Properties Limited | Real estate | 2002 |
| Miflexit Ltd | Wholesale & retail | 2023 |
| Mightus Transport Ltd | Transport & logistics | 2023 |
| Mighty Grappler Ltd | Wholesale & retail | 2026 |
| Mighty Services UK Ltd | Wholesale & retail | 2023 |
| Migtigarc Limited | Wholesale & retail | 2004 |
| Mihai Cotoc Ltd | Transport & logistics | 2019 |
| Mihejevpromotions Ltd | Wholesale & retail | 2024 |
| Mikana Assetshare Ltd | Real estate | 2020 |
| Mike Benwell Ltd | Hospitality | 2019 |
| Mike Shop Limited | Wholesale & retail | 2025 |
| Mike Sullivan Entertainments Limited | Arts & recreation | 2003 |
| Miki Carpentry Limited | Manufacturing | 2019 |
| Mila's Coffee Lounge Ltd | Hospitality | 2024 |
| Milan Home Style Ltd | Wholesale & retail | 2025 |
| Milano Barber Ltd | Other services | 2019 |
| Milanogarden Ltd | Hospitality | 2024 |
| Mild IOW Limited | Hospitality | 2026 |
| Milia Projects Ltd | Professional & scientific | 2024 |
| Military Road Car Sales Limited | Wholesale & retail | 2025 |
| Mill Gardens Management (Wickham) Limited | Households | 1996 |
| Millan Healthcare Services Ltd | Professional & scientific | 2017 |
| Millbrooke Limited | Hospitality | 2000 |
| Miller Muir Ltd | Wholesale & retail | 2025 |
| Miller&Paget Leisure Limited | Hospitality | 2020 |
| Millhouse Residents Association Limited | Administrative & support | 1972 |
| Million Soul Limited | Wholesale & retail | 2009 |
| Mills Professional Services Ltd | Health & social care | 2016 |
| Milton Garage 143 Ltd | Wholesale & retail | 2024 |
| Milton Park Properties Limited | Real estate | 2018 |
| Milton Road Yard Ltd | Real estate | 2024 |
| Mimi & Marble Holdings Limited | Financial services | 2022 |
| Mimi & Marble Investments Limited | Financial services | 2022 |
| Mindset Maintenance CIC | Administrative & support | 2023 |
| Mindworks Laboratories Limited | Information & communication | 2013 |
| Minerva Aesthetics Professionals Limited | Health & social care | 2025 |
| Mini Moony Ltd | Other services | 2024 |
| Mini Robot Limited | Information & communication | 2011 |
| Mini Stop Ltd Ltd | Hospitality | 2024 |
| Minimax Ventures Limited | Real estate | 2015 |
| MINKOV3 Ltd | Hospitality | 2019 |
| Mint Marketing Agency Ltd | Professional & scientific | 2023 |
| Mintspeed Limited | Information & communication | 1984 |
| Minzaminia Ltd | Wholesale & retail | 2020 |
| Mirage SRM Ltd | Wholesale & retail | 2025 |
| Mirror Magic Hand Car Wash Ltd | Professional & scientific | 2024 |
| Misco Consultancy Limited | Professional & scientific | 2022 |
| Misho Global Ltd | Wholesale & retail | 2020 |
| Mission Agency Limited | Administrative & support | 2018 |
| Mister&Remoj Limited | Other services | 2018 |
| Misworx Limited | Information & communication | 2018 |
| Mitch's Munch Box Ltd | Hospitality | 2019 |
| Mitchard Hair & Beauty Limited | Other services | 2009 |
| Mitchbourne Medical Services Limited | Health & social care | 2015 |
| Mitchell & Stones Limited | Professional & scientific | 2018 |
| Mitchell and James (Caravans) Limited | Wholesale & retail | 1997 |
| Mitchell Point M.C. Limited | Households | 1989 |
| Mitre Construction Management Limited | Administrative & support | 2020 |
| Mitre Court (Fareham) Management Limited | Households | 1978 |
| Mitsi Art Ltd | Wholesale & retail | 2009 |
| Miura Architecture Limited | Professional & scientific | 2026 |
| MJ Building Maintenance & Projects Limited | Construction | 2023 |
| MJ Food & Beverage Ltd | Hospitality | 2025 |
| MJ Yachting Ltd | Administrative & support | 2012 |
| MJB Holdings (South) Limited | Professional & scientific | 2022 |
| MJC Rail Services Ltd | Construction | 2017 |
| MJH Building Consultants Limited | Construction | 2017 |
| MJH Installations Limited | Construction | 2005 |
| MJK Developments Ltd | Construction | 2018 |
| Mjkh Ltd | Real estate | 2022 |
| Mjkr Consulting Limited | Professional & scientific | 2024 |
| MJL Electrical Ltd | Construction | 2005 |
| MJR Contract Services Ltd | Administrative & support | 2024 |
| Mjrm Construction Ltd | Construction | 2026 |
| Mjwarduk Limited | Information & communication | 2009 |
| MK Southsea Ltd | Real estate | 2020 |
| MK21 Engineering Solutions Limited | Manufacturing | 2017 |