| Lords Consultancy Services Ltd | Information & communication | 2019 |
| Lost Marble Brickwork Ltd. | Construction | 2016 |
| Loughglynn Limited | Professional & scientific | 2013 |
| Loved Ones Funerals Ltd | Other services | 2019 |
| Lovemamaison Limited | Wholesale & retail | 2021 |
| LOW Carbon Alliance Development Services Ltd | Construction | 2021 |
| Loxham Limited | Information & communication | 2026 |
| Loxley Developments Ltd | Construction | 2025 |
| Loxley Stables Management Limited | Households | 2018 |
| LSJ the Car Body Repair Specialist Ltd | Wholesale & retail | 2016 |
| LTS Audit Risk and Control Solutions Ltd | Administrative & support | 2017 |
| Lucky Lobster Art Ltd | Arts & recreation | 2025 |
| Lulaca Properties Limited | Real estate | 2025 |
| Lumo Ltd | Information & communication | 2014 |
| Lunic Ltd | Professional & scientific | 2020 |
| Lusso Aviation Limited | Professional & scientific | 2019 |
| Luton Environmental Limited | Construction | 2011 |
| Luxuria Lifestyle International Limited | Administrative & support | 2016 |
| Luxury Holidays (Cotswolds) Limited | Real estate | 2010 |
| Luxury Nails 42 Ltd | Other services | 2023 |
| Lydian HR Ltd | Administrative & support | 2025 |
| M & D Fine Turf Spraying Ltd | Administrative & support | 2020 |
| M Cooper Scenery Limited | Construction | 2017 |
| M D & D a Property Development Ltd | Construction | 2021 |
| M S Sagoo Ltd | Professional & scientific | 2022 |
| M T Loos Limited | Other services | 2008 |
| M1 Transport Services Ltd | Administrative & support | 2021 |
| MA UK Services Ltd | Professional & scientific | 2019 |
| Macca Investments Limited | Real estate | 2021 |
| Mackenzie Electrical (London) Ltd | Construction | 2018 |
| Macs Project Services Limited | Information & communication | 2026 |
| Made in Calcutta Ltd | Information & communication | 2022 |
| Made With Tonic Ltd | Professional & scientific | 2020 |
| Magfour Investments Limited | Administrative & support | 2009 |
| Maggie J.Jewellers Ltd | Wholesale & retail | 2012 |
| Magnets 4 Health Limited | Wholesale & retail | 2003 |
| Maher & Baxter Ltd | Construction | 2021 |
| Mainham Ltd | Professional & scientific | 2020 |
| Mainline Health & Safety Management Ltd | Professional & scientific | 2019 |
| Mainly Money Limited | Financial services | 2026 |
| Mainly Mortgages Limited | Financial services | 2017 |
| Maintain Improve Ltd | Construction | 2020 |
| Make IT Happen Signage Academy Limited | Education | 2023 |
| Make IT Happen Signage Consultancy Ltd | Professional & scientific | 2016 |
| Manor Farm (Marsworth) Equestrian Limited | Other services | 2020 |
| Manor Medical Group Ltd | Other services | 2026 |
| Mansfield IT Services Limited | Information & communication | 2023 |
| Mansi Building & Renovations Ltd | Construction | 2014 |
| Manticore Technologies Limited | Information & communication | 2020 |
| Marash Developments Limited | Wholesale & retail | 1981 |
| Margisal Limited | Real estate | 1977 |
| Maria Verde Ltd | Hospitality | 2021 |
| Marino Software Limited | Information & communication | 2020 |
| Mark Kettle IT Solutions Limited | Information & communication | 2010 |
| Mark Verney Limited | Administrative & support | 2003 |
| Marquant Limited | Professional & scientific | 2015 |
| Marshalls Paving and Landscaping Limited | Professional & scientific | 2026 |
| Marsp Property Maintenance Ltd | Construction | 2020 |
| Marsworth Steam Rally Community Interest Company | Arts & recreation | 2016 |
| Marsworth Wharf Management Co Limited | Real estate | 2015 |
| Masons Minibus & Coach Hire Ltd | Transport & logistics | 2015 |
| Masons Stores Ltd | Wholesale & retail | 2015 |
| Matilda Newco Limited | Professional & scientific | 2013 |
| Matilda's Planet Ltd | Manufacturing | 2020 |
| Matrix Handling Limited | Wholesale & retail | 1995 |
| Matt Arnold Ltd | Information & communication | 2019 |
| Maven CAD Ltd | Information & communication | 2017 |
| MAX Squared Studios Ltd | Information & communication | 2023 |
| Maxana Films Limited | Information & communication | 2024 |
| Maydell Property Ltd | Professional & scientific | 2015 |
| Mayfair Bathrooms London Ltd | Construction | 2022 |
| Mayland Consulting Limited | Professional & scientific | 2020 |
| MB Carpentry and Building Ltd | Construction | 2015 |
| MB Lining Limited | Construction | 2011 |
| Mcalit Ltd | Information & communication | 2019 |
| Mcgeough & Sons Limited | Construction | 2013 |
| Mcghin Consulting Limited | Professional & scientific | 2026 |
| Mckane Travel Group Ltd | Administrative & support | 2024 |
| Mcqueen Marketing Ltd | Professional & scientific | 2025 |
| Mead Consultants Limited | Information & communication | 2017 |
| Meakes Ltd | Professional & scientific | 2021 |
| Mechsmith Ltd | Professional & scientific | 2025 |
| Medcentral Ltd | Information & communication | 2014 |
| Medisure GP Services Ltd | Administrative & support | 2022 |
| Medisure Locums Ltd | Administrative & support | 2022 |
| Meerkat Marquees 2025 Limited | Administrative & support | 2025 |
| Mega Load Ltd | Construction | 2021 |
| MEM Technology Ltd | Information & communication | 2020 |
| Mentmore Historics Ltd | Professional & scientific | 2022 |
| Meridian Stamp Company Ltd | Wholesale & retail | 2003 |
| Meridian Stonegate Services Ltd | Professional & scientific | 2026 |
| Merrybert Limited | Professional & scientific | 2023 |
| Metallum Anglia Limited | Professional & scientific | 2017 |
| Metman Enterprises Limited | Real estate | 1970 |
| Metric Media Ltd | Professional & scientific | 2011 |
| MGP Bookkeeping Services Ltd | Professional & scientific | 2025 |
| MHB Business Services Limited | Administrative & support | 2016 |
| MHK Consulting Limited | Information & communication | 2018 |
| MI Construction Bedford Ltd | Construction | 2020 |
| Michael Collins Ltd | Households | 2025 |