| Morriston Ground Rents Limited | Real estate | 2021 |
| Morriston Heritage Properties Limited | Real estate | 2020 |
| Morriston M & D Barber Ltd | Other services | 2025 |
| Morriston Market Ltd | Wholesale & retail | 2025 |
| Morriston Pharm Limited | Health & social care | 2016 |
| Morriston Three Piece Suite Centre Limited | Wholesale & retail | 1982 |
| Morriston Turret Limited | Hospitality | 2019 |
| Morriston Vape Shop Ltd | Wholesale & retail | 2022 |
| Morriston Vapes Ltd | Wholesale & retail | 2025 |
| Morse Law Limited | Professional & scientific | 2012 |
| Morse Vending Ltd | Wholesale & retail | 2025 |
| Morstone Build Co Ltd | Construction | 2025 |
| Morter Group Ltd | Hospitality | 2026 |
| Mortgage Advice Swansea Limited | Financial services | 2016 |
| Mortgage Advisers-Uk Ltd | Financial services | 2025 |
| Mortgage Finder-Wales Limited | Financial services | 2019 |
| Morzuo (Holdings) Limited | Financial services | 2024 |
| Morzuo 2 Limited | Real estate | 2024 |
| Morzuo Limited | Real estate | 2016 |
| MOS Group Ltd | Real estate | 2021 |
| Mosaic Operations Ltd | Professional & scientific | 2021 |
| Moss and Maple Play Cafe Ltd | Hospitality | 2025 |
| MOT and Clutch Specialists Ltd | Wholesale & retail | 2016 |
| Motion Compliance Limited | Professional & scientific | 2017 |
| Motion Tents Ltd | Manufacturing | 2025 |
| Motley Gowerton Ltd | Manufacturing | 2020 |
| Motley Holdings Ltd | Financial services | 2025 |
| Motley Pontarddulais Ltd | Manufacturing | 2025 |
| Motley Tenby Ltd | Manufacturing | 2025 |
| Motobroz Ltd | Other services | 2025 |
| Motor City (Wales) Limited | Extraterritorial | 2004 |
| Motor ME Ltd | Wholesale & retail | 2021 |
| Motor Park Limited | Real estate | 2021 |
| Motorcycle Training (Wales) Limited | Education | 2005 |
| Motorplex U.K Ltd | Wholesale & retail | 2022 |
| Motr Limited | Wholesale & retail | 2026 |
| Mount (Management) Limited (the) | Real estate | 1971 |
| Mount Pleasant (SA1 6EF) Property Limited | Real estate | 2004 |
| Mount Pleasant Business Centre Ltd | Other services | 2025 |
| Mount Pleasant Food & Wine Ltd | Wholesale & retail | 2026 |
| Mountain People Wine / Gwin Pobl Y Mynydd Ltd | Wholesale & retail | 2025 |
| Move IT Transport Limited | Transport & logistics | 1997 |
| Move on Lettings Ltd | Real estate | 2024 |
| Move on UP Property Limited | Real estate | 2021 |
| Move Over Here Ltd | Real estate | 2021 |
| Moventum Limited | Administrative & support | 2025 |
| Moveopoly Ltd | Real estate | 2025 |
| Moving Vision Limited | Information & communication | 1992 |
| Moving YOU Limited | Real estate | 2020 |
| MP Courier Services Ltd | Transport & logistics | 2019 |
| MPA Football Limited | Education | 2022 |
| Mpcr Limited | Wholesale & retail | 2007 |
| Mpen Ltd | Transport & logistics | 2022 |
| Mpfewings Ltd | Professional & scientific | 2012 |
| MPH Property Developers Ltd | Real estate | 2025 |
| MPM Wristbands Limited | Wholesale & retail | 2012 |
| MPR Interiors Limited | Construction | 2022 |
| MPS Demonstrator Project Limited | Manufacturing | 2023 |
| MPW (Swansea) Ltd | Real estate | 2020 |
| MPW (Swansea) OPS Ltd | Hospitality | 2020 |
| MQ Property Group Ltd | Real estate | 2024 |
| MR & MRS Walkies Ltd | Administrative & support | 2019 |
| MR Gadgil Ltd | Health & social care | 2011 |
| MR Kebab Porthcawl Ltd | Hospitality | 2025 |
| MR Michael Lewis Limited | Health & social care | 2019 |
| MR Peter Lewis Limited | Health & social care | 2019 |
| MR Sashin Ahuja Limited | Health & social care | 2004 |
| MR. Stairlift Limited | Extraterritorial | 1997 |
| MR. White's GIN Ltd | Manufacturing | 2021 |
| MRE. - Morgan Real Estate Limited | Real estate | 2023 |
| Mrflag (Flagpoles) Limited | Wholesale & retail | 2004 |
| Mrflag.Com Ltd | Manufacturing | 2010 |
| MRJ Developments Limited | Construction | 2018 |
| MRJ Phillips Limited | Hospitality | 2025 |
| MRM Management Consultancy Limited | Professional & scientific | 2007 |
| MRS Accidental Cook Ltd | Manufacturing | 2022 |
| MRS Addtobasket Limited | Professional & scientific | 2021 |
| MRS Bucket Cleaning Services Limited | Administrative & support | 2006 |
| MRS Bucket Property Limited | Real estate | 2018 |
| MRS Gleam Ltd | Administrative & support | 2026 |
| MRS Neat & MRS Tidy Limited | Administrative & support | 2021 |
| MRS Spotless Ltd | Administrative & support | 2026 |
| Mrss Food Ltd | Hospitality | 2024 |
| MS Catering Limited | Hospitality | 2019 |
| MS Food & Investment Limited | Hospitality | 2025 |
| MS Julian Building Services Limited | Construction | 2026 |
| MSA Engineering Services Limited | Construction | 2015 |
| MSK Radiology Limited | Health & social care | 2012 |
| MSL Asset Management Limited | Administrative & support | 2016 |
| MSL Bambu Propco Ltd | Financial services | 2026 |
| MSL Khalil Ltd | Real estate | 2025 |
| MSL Management Consulting Limited | Professional & scientific | 2017 |
| MSL Prop Co Ltd | Real estate | 2023 |
| MSL Uplands Prop Co Ltd | Real estate | 2026 |
| Msls Stretton Limited | Financial services | 2020 |
| MSS Mortgages Swansea Ltd | Financial services | 2017 |
| Msswansea Limited | Hospitality | 2024 |
| Mstfx Ltd | Wholesale & retail | 2024 |
| Mstm Ltd | Professional & scientific | 2014 |
| MT Hospitality Limited | Hospitality | 2018 |