| A&C Coastal Properties Ltd | Real estate | 2021 |
| A&D Carbon Solutions Ltd | Professional & scientific | 2013 |
| A&J Landscaping & Groundworks Limited | Administrative & support | 2021 |
| A&J Property Enterprises Limited | Real estate | 2006 |
| A&L Group Ltd | Real estate | 2023 |
| A&M Empire Limited | Real estate | 2021 |
| A&M Private Hire Limited | Transport & logistics | 2014 |
| A&R Property Development Ltd | Construction | 2023 |
| A-Fix Plumbing Ltd | Extraterritorial | 2019 |
| A-L-R Installation Group Ltd | Construction | 2025 |
| A-L-R Property Group Ltd | Households | 2025 |
| A-Sequence Limited | Information & communication | 2018 |
| A-Z C Stores Ltd | Wholesale & retail | 2010 |
| A. & B. Electrics Limited | Construction | 2002 |
| A. Bradshaw Property Solutions Ltd | Real estate | 2020 |
| A. Lloyd Electrical & Solar Limited | Construction | 2010 |
| A. W. (Hardwoods) Ltd. | Professional & scientific | 2005 |
| A.Beynon Agri Envirocon Limited | Construction | 2011 |
| A.Davies Group CYF. | Other services | 2025 |
| A.Dhillon Limited | Wholesale & retail | 2022 |
| A.G.A.A Investments Ltd | Construction | 2019 |
| A.I.Mills Ltd | Financial services | 2026 |
| A.L.Dudley Services Limited | Construction | 2017 |
| A.L.E.R.T. Activities Limited | Arts & recreation | 1999 |
| A.Sherwood Consultancy Ltd | Professional & scientific | 2024 |
| A1 Accountancy Solutions Ltd | Professional & scientific | 2012 |
| A1 Crushing Solutions Ltd | Mining & quarrying | 2013 |
| A1 Glass Repairs Ltd | Wholesale & retail | 2025 |
| A1 Guns Limited | Wholesale & retail | 2011 |
| A1 Home Emergency 247 Ltd | Other services | 2020 |
| A1 Resin Ltd | Construction | 2020 |
| A1K9 (London) Ltd | Other services | 2020 |
| A1K9 (UK) Ltd | Other services | 2020 |
| A1K9 International Limited | Other services | 2001 |
| A1K9 Limited | Other services | 2000 |
| A1K9 Protection Dogs Ltd | Other services | 2020 |
| A1K9 Security Limited | Other services | 2001 |
| A2Z 3 Property Limited | Real estate | 2026 |
| A2Z Digital Limited | Professional & scientific | 2023 |
| A2Z of Motoring Limited | Education | 2014 |
| A4Y Ltd | Wholesale & retail | 2024 |
| AA Catering Food Ltd | Wholesale & retail | 2014 |
| AA Cleaning & Maintenance Services Ltd | Administrative & support | 2023 |
| AA Cooling System Ltd | Manufacturing | 2021 |
| AA UK Building Services Limited | Construction | 2018 |
| Aabf Limited | Financial services | 2017 |
| Aabm Limited | Professional & scientific | 2014 |
| AAL E Abbas Tours Ltd | Administrative & support | 2024 |
| AAR Gower Holdings Limited | Financial services | 2022 |
| Aarrr Ltd | Hospitality | 2022 |
| Aart Limited | Arts & recreation | 2005 |
| Aartic Training Services Ltd | Administrative & support | 2012 |
| Aaru Group Ltd | Households | 2023 |
| Aaru Investment SPV Ltd | Construction | 2025 |
| Aathma Signals Limited | Wholesale & retail | 2025 |
| Aathmezhi Fuel Ltd | Wholesale & retail | 2024 |
| Aaum Ltd | Education | 2000 |
| AB Developments (South West) Ltd | Construction | 2025 |
| AB Group (Trading) Limited | Administrative & support | 2017 |
| AB Health, Safety and Environmental Solutions Limited | Professional & scientific | 2012 |
| AB Homebuild Ltd | Construction | 2025 |
| AB Solar Developments Ltd | Construction | 2025 |
| AB Solar GD Ltd | Construction | 2025 |
| AB Tyre and Aircon Services Limited | Wholesale & retail | 2026 |
| Abacus Sketty Holdings Limited | Financial services | 2025 |
| Abacus Sketty Road Limited | Education | 2004 |
| Abba Cabs Ltd | Transport & logistics | 2019 |
| Abbey Access Limited | Wholesale & retail | 2007 |
| Abbey Residential Agents Limited | Real estate | 2014 |
| Abbey Road SPV Ltd | Real estate | 2020 |
| Abbit Limited | Manufacturing | 1977 |
| Abbotts Brickwork Limited | Construction | 2018 |
| Abbydaas Limited | Health & social care | 2026 |
| ABC 24/7 Pest Control Ltd. | Administrative & support | 2012 |
| ABC Building Limited | Construction | 2025 |
| ABC Home Care and Improvements Ltd | Construction | 2019 |
| ABC of Money Limited | Administrative & support | 2016 |
| ABC Phonix Technology CYF | Information & communication | 2023 |
| ABC Wales ICF Ltd | Construction | 2018 |
| Abclonal UK Limited | Professional & scientific | 2021 |
| Abco Europe Ltd | Extraterritorial | 2021 |
| Abco Group Ltd | Wholesale & retail | 2021 |
| Abco Healthcare Ltd | Wholesale & retail | 2021 |
| Abco Holdings Ltd | Financial services | 2024 |
| Abco Hygiene Ltd | Wholesale & retail | 2021 |
| ABE Mechanical Limited | Professional & scientific | 2025 |
| Abeds Design and Engineering Limited | Professional & scientific | 2010 |
| Aber Eyes Ltd | Education | 2024 |
| Aber Landscapes Limited | Administrative & support | 2014 |
| Aber Vape Ltd | Wholesale & retail | 2025 |
| Abercrave Rugby Football Club Limited | Arts & recreation | 2017 |
| Aberfab Limited | Administrative & support | 2016 |
| Abergavenny Brake & Clutch Limited | Wholesale & retail | 2006 |
| Abergavenny Farm Supplies Limited | Extraterritorial | 2006 |
| Abergavenny Hand Surgery Limited | Health & social care | 2017 |
| Abermos Limited | Real estate | 2023 |
| Abernant Storage Ltd | Administrative & support | 2019 |
| Aberpro Limited | Real estate | 2005 |
| Abertawe & Gower Tree Surgery (2011) Ltd | Agriculture & fishing | 2011 |
| Abertawe Accountancy Services Limited | Professional & scientific | 1996 |