| JOE Osborne Racing Limited | Arts & recreation | 2015 |
| John Auckland Services Limited | Professional & scientific | 2022 |
| John Bailey Services Limited | Professional & scientific | 2021 |
| JON Bolton Developments Limited | Construction | 2013 |
| JP22 Ltd | Manufacturing | 2025 |
| JPE Contracts Ltd | Administrative & support | 2013 |
| JSO Trading Ltd | Wholesale & retail | 2016 |
| Julie Wilmer Accountancy Services Limited | Professional & scientific | 2015 |
| Jungle River Ltd | Wholesale & retail | 2019 |
| JYJ Management Consulting Ltd | Professional & scientific | 2022 |
| Kadean Limited | Extraterritorial | 2016 |
| KAIZEN247.CO.UK Ltd | Professional & scientific | 2023 |
| Kamuy Engineering Ltd | Manufacturing | 2022 |
| Kanes of Granard Limited | Wholesale & retail | 2012 |
| Kanes of Granard Motors Limited | Education | 2005 |
| Kapro Ltd | Information & communication | 2014 |
| KCC Services Limited | Real estate | 2018 |
| Keith Robinson Limited | Construction | 2017 |
| Kevin Smith Carpentry & Joinery Limited | Construction | 2015 |
| King Renewables Consulting Ltd | Professional & scientific | 2025 |
| Kingfisher Landscapes (MK) Limited | Administrative & support | 2021 |
| Kitch Engineering Ltd | Professional & scientific | 2018 |
| Kitpac Limited | Extraterritorial | 2016 |
| Krama Ltd | Administrative & support | 2018 |
| KS Studio Services Ltd | Construction | 2024 |
| Kube Projects Ltd | Wholesale & retail | 2020 |
| KUH Solutions Ltd | Professional & scientific | 2005 |
| L & W Events Ltd | Hospitality | 2023 |
| Lapel Ltd | Professional & scientific | 2026 |
| Laura Randall Ltd | Information & communication | 2015 |
| Lavendon FM Limited | Professional & scientific | 2023 |
| Lavendon Ltd | Professional & scientific | 2007 |
| Leese Spaceflight Project Management Ltd | Professional & scientific | 2015 |
| Leinster Plant Hire and Sales Ltd | Hospitality | 2015 |
| LEO Antiques and Collectables Limited | Wholesale & retail | 2003 |
| LEO Bookkeeping Services Ltd | Professional & scientific | 2019 |
| LEO Commercial Property Ltd | Real estate | 2025 |
| LES Postawa Associates Limited | Professional & scientific | 2019 |
| Less Grid Ltd | Construction | 2026 |
| Levett & Associates Ltd | Professional & scientific | 2013 |
| LG Talent Ltd | Administrative & support | 2020 |
| Libabun Business Angels Limited | Professional & scientific | 2013 |
| Libby Delaney Interiors Ltd | Professional & scientific | 2026 |
| Linesoft Solutions Limited | Information & communication | 2009 |
| Lisa MAY Training Ltd | Information & communication | 2023 |
| Little Hermitage Ltd | Hospitality | 2023 |
| Litton Consultants Limited | Professional & scientific | 2020 |
| LM Automotive Limited | Wholesale & retail | 2022 |
| Lock and Load Self-Storage Limited | Transport & logistics | 2026 |
| Loknok Ltd | Financial services | 2023 |
| LRM Fitness Ltd | Arts & recreation | 2023 |
| LW Architecture Ltd | Professional & scientific | 2020 |
| M D Environmental Surveys Ltd | Professional & scientific | 2024 |
| M P M Wall & Floor Tiling Limited | Construction | 2005 |
| M Simpson Associates Ltd | Professional & scientific | 2004 |
| M.G Consultancy Ltd | Financial services | 2026 |
| M.T Estate Holdings Ltd | Real estate | 2026 |
| Macdonald Steels Limited | | 1982 |
| Magpie Publishing Ltd | Information & communication | 2009 |
| Maple (453) Limited | Households | 2019 |
| Maplewills Limited | Financial services | 2020 |
| Marcus Jordan & Co Limited | Real estate | 2002 |
| Margaret James Estate Agents Ltd | Real estate | 2018 |
| Marian Systems Engineering Ltd | Information & communication | 2012 |
| Marketing Works Ltd | Administrative & support | 2025 |
| Mask Fitting and Testing Ltd | Professional & scientific | 2025 |
| Matt Fyson Props Ltd | Information & communication | 2026 |
| MCF Aviation Limited | Transport & logistics | 2019 |
| MCF Property Limited | Real estate | 2018 |
| Mcma Ltd | Professional & scientific | 2022 |
| Melio Digital Limited | Information & communication | 2019 |
| MEM Digital Ltd | Information & communication | 2021 |
| Mercury Safety Products Limited | Manufacturing | 1994 |
| Metasense Limited | Information & communication | 2024 |
| Metrosigns 2000 (Bedford) Limited | Manufacturing | 2002 |
| MIA Communications Limited | Professional & scientific | 2010 |
| Mike Clarke Consulting Limited | Professional & scientific | 2019 |
| Mill Lane PTN Limited | Real estate | 2020 |
| Milton Keynes Commercial Vehicle Repairs Limited | Wholesale & retail | 2006 |
| Mind Body BE Ltd | Health & social care | 2011 |
| MIS Consultants Ltd | Information & communication | 2024 |
| MK Horsebox Repairs Ltd | Manufacturing | 2015 |
| MK Pulse Limited | Information & communication | 2015 |
| Moneycore Asset Management Limited | Financial services | 2012 |
| Monica Grady Meteorite Lady Limited | Education | 2016 |
| MOO MOO Services Limited | Hospitality | 2003 |
| Motte Bailey Castle Limited | Households | 2013 |
| Moulton Scaffolding Services Limited | Construction | 2015 |
| MS Constructions Limited | Construction | 2009 |
| MTJ Desserts Ltd | Hospitality | 2023 |
| Muir Care Ltd | Public administration | 2022 |
| Multiplex UK Install Limited | Construction | 2015 |
| Mylo Industrial Design Limited | Professional & scientific | 2008 |
| Naga Mirchi Ltd | Hospitality | 2025 |
| Napier Real Estate Ltd | Real estate | 2020 |
| Nationwide Finance Limited | Financial services | 2019 |
| Neet Group (Olney) Limited | Construction | 2021 |
| Neet Maintenance Limited | Construction | 2021 |
| Nestiq Ltd | Real estate | 2025 |
| New City Furniture Limited | Manufacturing | 2015 |