| Miles Byron Ltd | Real estate | 2020 |
| Miles Taekwondo LLP | | 2015 |
| Milestone FS Ltd | Administrative & support | 2018 |
| Milestone Laboratories Ltd | Manufacturing | 2025 |
| Milestone Product Development Limited | Professional & scientific | 2021 |
| Mill Court Property Group Ltd | Real estate | 2025 |
| Miller Hare Limited | Information & communication | 1992 |
| Miller James Financial Planning Limited | Professional & scientific | 2014 |
| Millergreen Ltd | Professional & scientific | 2018 |
| Millets Farm Centre Limited | Wholesale & retail | 2014 |
| Millets Farm Shop Limited | Wholesale & retail | 2007 |
| Millets Playbarn Limited | Arts & recreation | 2017 |
| Millhouse Services Limited | Professional & scientific | 2025 |
| Mills Property Collective Ltd | Real estate | 2025 |
| Miltax Financial Brokers Ltd | Administrative & support | 2018 |
| Miltax Ltd | Professional & scientific | 2013 |
| Miltax Property Ltd | Real estate | 2025 |
| Milton Regent Limited | Real estate | 2016 |
| Milton Road FA Ltd | Health & social care | 2022 |
| Milton Road Surgery Enterprise Ltd | Health & social care | 2022 |
| Milton Road Swindon (Number 1) Management Company Limited | Households | 2010 |
| Milubo Transport Ltd | Transport & logistics | 2020 |
| Mimi & Coco Ltd | Transport & logistics | 2025 |
| Mimo Doce Ltd | Manufacturing | 2025 |
| Mind Your Life Ltd | Health & social care | 2018 |
| Mind,Body and Soul Care Services Limited | Health & social care | 2025 |
| Mindbodyfusion Ltd | Education | 2024 |
| Mindful Movement the Brand Limited | Wholesale & retail | 2023 |
| Mindful Supported Living Limited | Health & social care | 2023 |
| Mindisity Ltd | Health & social care | 2015 |
| Mindtree Software Solutions Ltd | Information & communication | 2018 |
| Minerva Cleaning Ltd | Administrative & support | 2006 |
| Minerva Properties Ltd | Real estate | 2017 |
| Minerva Stericlean Ltd | Wholesale & retail | 2016 |
| Mineshock Labs Ltd | Information & communication | 2025 |
| Minety Contractors Limited | | 1974 |
| Ming Mart Ecommerce Ltd | Information & communication | 2017 |
| Mingora Ltd | Hospitality | 2025 |
| Mini Steamers Childcare Limited | Health & social care | 2023 |
| Ministate Media Limited | Administrative & support | 2013 |
| Minster Granite Limited | Professional & scientific | 2025 |
| Mint Island Limited | Professional & scientific | 2017 |
| Minty Water Ltd | Information & communication | 2016 |
| MIR Barbers Ltd | Other services | 2019 |
| Mira Property Solutions Ltd | Real estate | 2021 |
| Mira'Supreme Ltd | Transport & logistics | 2020 |
| Miran Haulage Limited | Other services | 2008 |
| Miribeth Limited | Real estate | 2019 |
| Miscado Ltd | Wholesale & retail | 2025 |
| Miss Sport Ltd | Education | 2025 |
| Mission Pest Control Ltd | Agriculture & fishing | 2022 |
| Mister Shine Limited | Administrative & support | 2017 |
| Mistral Dental Care Limited | Health & social care | 2010 |
| Mistral Publishing Services Limited | Arts & recreation | 2025 |
| MIT Cricketers Enterprise Ltd | Administrative & support | 2021 |
| Mitchell Cycles Group Limited | Wholesale & retail | 2024 |
| Mitek Retail Ltd | Professional & scientific | 2013 |
| Mithai House Limited | Wholesale & retail | 2025 |
| Mittal Services Ltd | Transport & logistics | 2024 |
| Mitztags Ltd | Manufacturing | 2026 |
| MJ Byford Ltd | Financial services | 2026 |
| MJ Plumbing & Tiling Ltd | Construction | 2021 |
| MJ Rosario Limited | Health & social care | 2017 |
| MJ Solutions Services Limited | Construction | 2021 |
| MJB Compliance Ltd | Professional & scientific | 2024 |
| MJB Fire Systems Limited | Administrative & support | 2016 |
| MJC Partitions & Ceilings Limited | | 2009 |
| MJD Pipework Services Limited | Construction | 2016 |
| MJF and SJF Leisure Ltd | Hospitality | 2011 |
| MJF CAD Solutions Ltd | Professional & scientific | 2022 |
| MJG Builders Limited | Construction | 2025 |
| MJH Projects Ltd | Construction | 2024 |
| MJH Technology Limited | Information & communication | 2012 |
| MJL Property & Lettings Ltd | Real estate | 2026 |
| MJN Sports LLP | | 2019 |
| MJQ Services Limited | Information & communication | 2002 |
| MJS Encapsulation Ltd | Manufacturing | 2016 |
| MJT Capital Holdings Ltd | Financial services | 2025 |
| MJT Utility Services Ltd | Construction | 2026 |
| MK Engineering Limited | Information & communication | 2025 |
| MK House Lettings Ltd | Real estate | 2022 |
| MK Sites Ltd | Manufacturing | 2026 |
| MK Tiling Ltd | Construction | 2022 |
| MK Worldwide Holdings Limited | Wholesale & retail | 2013 |
| Mkgr Ltd | Transport & logistics | 2018 |
| MKL Groundworks Ltd | Construction | 2023 |
| Mkms Training Services Ltd | Education | 2020 |
| ML Wind LLP | | 2013 |
| Mlcosmetics Limited | Wholesale & retail | 2026 |
| MM Financial Limited | Professional & scientific | 2025 |
| MM Optics Ltd | Health & social care | 2014 |
| MM Project Production Ltd | Administrative & support | 2020 |
| MM Solutions Limited | Information & communication | 2004 |
| MM265 Ltd | Hospitality | 2026 |
| Mmaatt Limited | Information & communication | 2019 |
| Mmdj Ltd | Transport & logistics | 2022 |
| Mmgte Ltd | Professional & scientific | 2022 |
| MMI Swindon Ltd | Wholesale & retail | 2025 |
| Mmiri Swim Ltd | Wholesale & retail | 2023 |
| MMK Trans Ltd | Transport & logistics | 2014 |