| Aquarod Drainage Services Ltd | Administrative & support | 2017 |
| Aquatic World (Cardiff) Limited | Wholesale & retail | 2015 |
| Aquilla Court Limited | Households | 1976 |
| Aquilla Group Limited | Financial services | 2022 |
| Aquilla Products Limited | Wholesale & retail | 2020 |
| Aquino Coating Services Ltd | Manufacturing | 2022 |
| Aquino Properties Limited | Real estate | 2024 |
| AR Amser Ltd | Professional & scientific | 2019 |
| AR Cardiff Ltd | Wholesale & retail | 2026 |
| AR Construction Management Limited | Professional & scientific | 2024 |
| AR Eyecare Limited | Health & social care | 2009 |
| AR House Builders Limited | Construction | 2025 |
| AR Investment Holdings Ltd | Transport & logistics | 2020 |
| AR Micro System Limited | Information & communication | 2019 |
| AR Platinum Chauffeurs Limited | Administrative & support | 2020 |
| AR Point Limited | Wholesale & retail | 2024 |
| AR Retail Solutions Ltd | Manufacturing | 2022 |
| AR Supermart Ltd | Wholesale & retail | 2025 |
| AR UK Cars Limited | Wholesale & retail | 2018 |
| AR80 Property Ltd | Households | 2022 |
| ARA Properties (Cardiff) Ltd | Construction | 2014 |
| Araali and Sons Holding Company Limited | Financial services | 2025 |
| Arab Tourism Magazine Ltd | Information & communication | 2025 |
| Arab Zens Ltd. | Wholesale & retail | 2024 |
| Arab-African Union for Economic Integration and Joint Cooperation Ltd | Information & communication | 2021 |
| Arabella Catering Ltd | Hospitality | 2013 |
| Arabella Equestrian Limited | Wholesale & retail | 2020 |
| Arabian Hund Ltd | Wholesale & retail | 2025 |
| Arabic School of Cardiff Limited | Education | 2023 |
| Arabtax Ltd | Professional & scientific | 2025 |
| Arabtweaks Ltd | Information & communication | 2025 |
| Arabyworld Ltd | Wholesale & retail | 2025 |
| Arad Consulting Limited | Professional & scientific | 2004 |
| Aradus Ltd | Wholesale & retail | 2025 |
| Arafama Ltd | Wholesale & retail | 2025 |
| Arafat Miah Ltd | Information & communication | 2022 |
| Araford Limited | Households | 1972 |
| Aralia Studios Limited | Education | 2022 |
| Aram 1 Properties Ltd | Real estate | 2025 |
| Aramworks Limited | Information & communication | 2020 |
| Arana Entertainment Group Ltd | Information & communication | 2018 |
| Arancio Property Ltd | Real estate | 2021 |
| Arani Convenience Store Ltd | Wholesale & retail | 2025 |
| Aranletobarbers Limited | Other services | 2025 |
| Aranoia Ltd | Professional & scientific | 2012 |
| Ararkis Automobili Ltd. | Wholesale & retail | 2024 |
| Aratsh Ltd | Manufacturing | 2024 |
| Araz Premium Limited | Wholesale & retail | 2024 |
| Arazi Limited | Agriculture & fishing | 2014 |
| ARB Global Trading Ltd | Wholesale & retail | 2024 |
| Arbab Premier Ltd | Wholesale & retail | 2025 |
| Arbitrium Consulting Limited | Information & communication | 2016 |
| Arbnix Limited | Financial services | 2026 |
| Arbo Transport Limited | Transport & logistics | 2014 |
| Arbor Vale (Dinas Powys) Limited | Real estate | 2018 |
| Arbor-Craft Timber Titans Road & Rail Maintenance UK Limited | Wholesale & retail | 2025 |
| Arbour Construction & Developments Ltd | Construction | 2023 |
| ARC - N11 Management Company Limited | Households | 2006 |
| ARC Atelier Group Limited | Construction | 2021 |
| ARC Atelier Limited | Real estate | 2018 |
| ARC Corporate Finance Brokers Ltd | Financial services | 2018 |
| ARC Education Consultancy Ltd | Education | 2025 |
| ARC Electrical Systems Ltd | Construction | 2021 |
| ARC Industrial Heating Limited | Professional & scientific | 2009 |
| ARC Mechanical Ltd | Construction | 2024 |
| Arcada Corporation PC | | 2017 |
| Arcade Didcot Ltd | Manufacturing | 2023 |
| Arcade JAM Ltd | Other services | 2024 |
| Arcade Publishers Ltd | Information & communication | 2025 |
| Arcade Wool Shop Ltd | Wholesale & retail | 2025 |
| Arcadia Cigars the Lanes Limited | Extraterritorial | 2022 |
| Arcadia Vision Ltd | Professional & scientific | 2018 |
| Arcadian Owls Productions Ltd | Information & communication | 2022 |
| Arcadian Supplies Ltd | Wholesale & retail | 2017 |
| Arcadiax Ltd | Wholesale & retail | 2025 |
| Arcaig Limited | Construction | 2025 |
| Arcanine Services Limited | Professional & scientific | 2018 |
| Arcanum Reserve Limited | Wholesale & retail | 2025 |
| Arccrowd Ltd | Construction | 2017 |
| Arch Initiatives | Health & social care | 1993 |
| Arch IT Solutions Limited | Information & communication | 2012 |
| Arch Lighting Limited | Information & communication | 2009 |
| ARCH3D Ltd | Information & communication | 2018 |
| Archade Limited | Professional & scientific | 2012 |
| Archaic Rhyme Co., Limited | Wholesale & retail | 2020 |
| Archangel Construct Limited | Construction | 2019 |
| Archcore Architects Ltd | Construction | 2018 |
| Archer Property Agents Ltd | Real estate | 2017 |
| Archer Technology Group Ltd | Information & communication | 2022 |
| Archer Wells Limited | Professional & scientific | 2017 |
| Archer Wise Accountants & Auditors Limited | Professional & scientific | 2012 |
| Archetiera Limited | Construction | 2017 |
| Archie Gregory Associates Limited | Professional & scientific | 2020 |
| Architectural Building Supplies UK Ltd | Professional & scientific | 2024 |
| Architecture Design European Ltd | Manufacturing | 2013 |
| Architekten Haus Ltd | Administrative & support | 2018 |
| Archive Publications Limited | | 1985 |
| Archive Space Path Ltd | Information & communication | 2025 |
| Archview Management Limited | Households | 2011 |
| Archytas Corporate Planning Ltd | Financial services | 2018 |