| Altan Plumbing & Heating Ltd | Construction | 2021 |
| Altarvest Limited | Financial services | 2009 |
| Altec Systems Ltd | Manufacturing | 2011 |
| Altered Images (Swansea) Limited | Health & social care | 2012 |
| Alternative Precision Sheet Metal Limited | Manufacturing | 1997 |
| Altia Consultants Limited | Administrative & support | 2023 |
| Alumi Limited | Information & communication | 2023 |
| Aluna Life Ltd | Financial services | 2014 |
| Alwyn P John & SON Ltd | Professional & scientific | 2015 |
| ALX Construction Services Ltd | Construction | 2019 |
| AM Management Services Ltd | Professional & scientific | 2024 |
| AM Star Health Care (UK) Ltd | Health & social care | 2024 |
| Am&J Logistic Ltd | Transport & logistics | 2025 |
| AM2PM Lettings and Renovations Ltd | Real estate | 2020 |
| AMA Properties Ltd | Extraterritorial | 2011 |
| Aman Pharmacy (J.A.Jones) Limited | Wholesale & retail | 2011 |
| Amana Accountant Ltd | Financial services | 2022 |
| Amanda Walker Limited | Manufacturing | 2017 |
| Amanda's Home Support Ltd | Public administration | 2025 |
| Amara's Place Limited | Other services | 2025 |
| Amarok Building Services Ltd | Construction | 2022 |
| Amaryllis Management Ltd | Real estate | 2024 |
| Amaya Family Ltd | Hospitality | 2025 |
| Amazing Arts and Crafts Limited | Wholesale & retail | 2014 |
| Amazing Autos Ltd | Manufacturing | 2020 |
| Amazing Glazing (Wales) Ltd | Construction | 2003 |
| Amber & Pearl Limited | Arts & recreation | 2005 |
| Amber Environmental Consultancy Limited | Professional & scientific | 2012 |
| Amber Jones Assets & Management Ltd | Administrative & support | 2023 |
| Amber Lynn Limited | Real estate | 2024 |
| Amberley Properties Ltd | Real estate | 2001 |
| Ambia Ltd | Hospitality | 2022 |
| Ambience Kingston Ltd | Professional & scientific | 2022 |
| Ambo Accommodation Ltd | Hospitality | 2025 |
| Amcor Flexibles Distribution UK Limited | Administrative & support | 1969 |
| Amcor Flexibles Swansea Limited | Manufacturing | 2000 |
| AMD Comms Limited | Arts & recreation | 2019 |
| AMD Welding Ltd | Manufacturing | 2024 |
| Amdek Matrix Limited | Real estate | 1992 |
| Ameb Property Limited | Real estate | 2025 |
| Ameco Developments Limited | Construction | 2019 |
| Ameco Homes Limited | Real estate | 2024 |
| Ameco Leisure Group Limited | Professional & scientific | 1963 |
| Ameco Letting Limited | Hospitality | 2023 |
| Ameco Properties Limited | Real estate | 2008 |
| Amethyst Artificery Limited | Manufacturing | 2025 |
| Amfahh LEA Bridge Limited | Real estate | 2020 |
| AMH Renewables Ltd | Professional & scientific | 2023 |
| Amicable Ltd | Health & social care | 2019 |
| Amico Developments Limited | Administrative & support | 2004 |
| Amico Enterprises (Wales) Limited | Extraterritorial | 1996 |
| Amico Holdings Ltd | Construction | 2019 |
| Amima 94 Ltd | Hospitality | 2025 |
| Amju GAS Plumbing and Heating Ltd | Construction | 2023 |
| AMK Electrical Contractors Ltd | Construction | 2019 |
| AMK Foods Limited | Hospitality | 2020 |
| Amma Healthcare Ltd | Health & social care | 2020 |
| Ammaja Limited | Manufacturing | 2021 |
| Amman Health Care Limited | Health & social care | 2018 |
| Ammtas Limited | Professional & scientific | 2017 |
| AMN Prac Ltd | Health & social care | 2025 |
| AMN Properties Ltd | Real estate | 2019 |
| AMO Community for Authentic Growth CIC | Administrative & support | 2025 |
| AMO Operations Ltd | Hospitality | 2026 |
| Amodi Consulting Ltd | Professional & scientific | 2025 |
| AMP Design & Build Ltd | Construction | 2015 |
| AMP Housing Ltd | Real estate | 2025 |
| AMP Performance Engineering Limited | Wholesale & retail | 2019 |
| AMR & AMR Investments Limited | Financial services | 2022 |
| AMR Social Work Services Ltd | Health & social care | 2022 |
| Amroc Heating Services Limited | Construction | 2006 |
| AMS Spray Painting and Decorating Ltd. | Construction | 2019 |
| Amson Construction Limited | Real estate | 2006 |
| AMT Academy Ltd | Education | 2023 |
| Amusement Equipment Co.Limited | Hospitality | 1933 |
| Amwin Limited | Administrative & support | 2016 |
| AMY Dillwyn Management Company Ltd | Administrative & support | 2015 |
| AN Apple a Day (Health and Wellbeing) Community Interest Company | Health & social care | 2014 |
| AN JU Property Ltd | Real estate | 2022 |
| ANA Metalo Trading Ltd | Wholesale & retail | 2024 |
| Anaa PVT Ltd | Wholesale & retail | 2024 |
| Anacoders Ltd | Information & communication | 2019 |
| Analysispro Limited | Information & communication | 2011 |
| Anarkali (Swansea) Ltd | Hospitality | 2017 |
| Anastasia Property Ltd | Real estate | 2015 |
| Anatolia Kitchen Ltd | Hospitality | 2019 |
| Anawaz Limited | Health & social care | 2025 |
| Anca Property Ltd | Real estate | 2022 |
| Anchor Bay Management Limited | Households | 1993 |
| Anchor Court Management Company (Swansea) Limited | Households | 1984 |
| Anchor Crown Ltd | Households | 2024 |
| Andeburg Ltd | Financial services | 2023 |
| Ander Commercial Services Limited | Professional & scientific | 2022 |
| Ander Financial Services Limited | Financial services | 2017 |
| Anderly Property Investments Ltd | Real estate | 2019 |
| Anderly Property Solutions Limited | Real estate | 2019 |
| Anderson Investments Group Ltd | Professional & scientific | 2025 |
| Andrew D'Auria Solutions Limited | Construction | 2010 |
| Andrew Durber Properties Ltd | Construction | 2024 |
| Andrew Evans Painting Contractors Limited | Construction | 1999 |