| Actionzone Rentals Limited | Real estate | 2025 |
| Active Psychological Solutions Limited | Health & social care | 2018 |
| Active Studies Limited | Professional & scientific | 2017 |
| Active Thread Ltd | Information & communication | 2002 |
| Active Wellbeing Cwmcarn CIC | Arts & recreation | 2026 |
| Acumen Associate Financial Services Ltd | Financial services | 2004 |
| Acumen Electronics Ltd | Manufacturing | 2025 |
| Acvs Maintenance Limited | Construction | 2016 |
| ACW Draincare Ltd | Construction | 2022 |
| AD Eco Services Ltd | Other services | 2022 |
| AD8 Promotions Ltd | Arts & recreation | 2021 |
| AD8 Properties Ltd | Real estate | 2023 |
| Adam Arab Food Ltd | Hospitality | 2023 |
| Adam Barbers Ltd | Other services | 2014 |
| Adam Davies Car Sales Limited | Wholesale & retail | 2021 |
| Adam Frampton Plant Hire Limited | Administrative & support | 2003 |
| Adam Peter Construction Ltd | Construction | 2023 |
| Adam Ranford Electrical Ltd | Construction | 2025 |
| Adam&Marcin Ltd | Transport & logistics | 2016 |
| Adams and Adams Homes Ltd | Real estate | 2022 |
| Adams Eyecare Limited | Health & social care | 2003 |
| Adaptive Engineering Solutions Ltd | Professional & scientific | 2012 |
| Adaptive Software Solutions Limited | Information & communication | 2005 |
| Adclimb Ltd | Information & communication | 2017 |
| ADD Real Estate Ltd | Real estate | 2016 |
| Addition Building Limited | Construction | 2004 |
| ADE Fantasi Ltd | Extraterritorial | 2020 |
| ADE Mobile Tyres Ltd | Wholesale & retail | 2025 |
| Adeferedig CBC | Hospitality | 2025 |
| Adeken Limited | Health & social care | 2017 |
| Adelati Ltd | Wholesale & retail | 2024 |
| Ademt Limited | Financial services | 2013 |
| Adept Travel Limited | Transport & logistics | 2015 |
| Adeptomines Limited | Mining & quarrying | 2018 |
| ADF Farm Solutions UK Ltd | Information & communication | 2023 |
| Adfer Estates Limited | Hospitality | 2025 |
| Adinca Limited | Transport & logistics | 2016 |
| ADM Plant Training Ltd | Education | 2026 |
| Admiral Gardens Management Company Limited | Households | 1991 |
| ADO Empire LLP | | 2017 |
| ADO Options Ltd | Real estate | 2014 |
| Adobe Estates Ltd | Real estate | 2018 |
| Adopt a Chef Ltd | Hospitality | 2025 |
| Adre Properties Limited | Households | 2014 |
| Adrian Driving Services Ltd | Transport & logistics | 2013 |
| Adrian ISO Solutions Ltd | Professional & scientific | 2026 |
| Adroit Group Estates Limited | Real estate | 2024 |
| Adsay Limited | Administrative & support | 2025 |
| ADT Home Services Ltd | Construction | 2018 |
| ADT Leisure Limited | Arts & recreation | 2025 |
| Adultsy Limited | Wholesale & retail | 2025 |
| ADUN360 Limited | Real estate | 2023 |
| Advance Project Management Ltd | Professional & scientific | 2015 |
| Advanced Clinical Solutions Ltd | Professional & scientific | 2016 |
| Advanced Contracting Solutions Limited | Extraterritorial | 2013 |
| Advanced Contracts Solutions Limited | Construction | 2018 |
| Advanced Custom Engineering Ltd | Manufacturing | 2017 |
| Advanced Elastomer Systems Unlimited | Manufacturing | 1990 |
| Advanced Electrical Solar Solutions Limited | Extraterritorial | 2011 |
| Advanced Electrical Solutions Limited | Administrative & support | 2010 |
| Advanced Engineering (Newport) Ltd | Construction | 2018 |
| Advanced Mechanical Solutions (South Wales) Limited | Construction | 2016 |
| Advanced Performance Coatings Limited | Manufacturing | 2014 |
| Advanced Wall Coatings Limited | Construction | 2018 |
| Advancing Care Ltd. | Professional & scientific | 2012 |
| Adventure Digital Ltd | Professional & scientific | 2018 |
| Adventure in Business Ltd | Extraterritorial | 2015 |
| ADW Blades Limited | Administrative & support | 2026 |
| ADZ Travel Solutions Ltd | Administrative & support | 2025 |
| AE Estate Planning Limited | Other services | 2022 |
| AE Global Events & Experiences Limited | Professional & scientific | 2026 |
| AE Petersen Limited | Wholesale & retail | 2010 |
| Aegis Homes Ltd | Health & social care | 2016 |
| Aegis Security Limited | Administrative & support | 2014 |
| Aeiou Limited | Administrative & support | 2015 |
| Aelwyd Build Ltd | Construction | 2026 |
| Aerfin Holdings Limited | Transport & logistics | 2014 |
| Aerfin Limited | Transport & logistics | 2010 |
| Aerial & Satellite Services Ltd | Information & communication | 2026 |
| Aerial Innovation Limited | Manufacturing | 2024 |
| Aermach Group Limited | Financial services | 2020 |
| Aermach Limited | Wholesale & retail | 2017 |
| Aerugo Limited | Arts & recreation | 2014 |
| Aerugo Properties Limited | Real estate | 2019 |
| Aesthetics by G Ltd | Other services | 2024 |
| Aether Aerospace Ltd | Manufacturing | 2022 |
| Aetherion Engineering Ltd | Construction | 2025 |
| Aeturnum College of Embalming Ltd | Other services | 2022 |
| AF03 Ltd | Arts & recreation | 2025 |
| AFA Architects and Planners Ltd | Professional & scientific | 2012 |
| AFD Ltd | Real estate | 2017 |
| Afema Properties Ltd | Real estate | 2025 |
| Affempreneurs Ltd | Education | 2025 |
| Affinity Compliance Solutions Ltd | Administrative & support | 2014 |
| Affordable Prestige Cars South Wales Ltd | Wholesale & retail | 2025 |
| Affordable Tree and Garden Limited | Administrative & support | 2025 |
| Afix Engineering Ltd | Manufacturing | 2020 |
| AFM Industries Limited | Construction | 2003 |
| AFO Group Ltd | Real estate | 2019 |
| Afph Holdings Limited | Financial services | 2021 |