| Attention Care Ltd | Health & social care | 2020 |
| Attest-Labs Limited | Professional & scientific | 2013 |
| Attie Limited | Health & social care | 2015 |
| Attire Ltd | Wholesale & retail | 2025 |
| Attract Recruitment Ltd | Administrative & support | 2011 |
| Attractive Products Ltd | Wholesale & retail | 2016 |
| Atua Ltd | Wholesale & retail | 2017 |
| Atumz Accountants Ltd | Wholesale & retail | 2023 |
| Atuogu Studios Ltd | Professional & scientific | 2021 |
| Atvi Properties Ltd | Real estate | 2024 |
| Atwrk Ltd. | Information & communication | 2018 |
| Auchinview Properties Limited | Real estate | 2026 |
| Aucott Developers Limited | Administrative & support | 1982 |
| Aucott Holdings Limited | Real estate | 1986 |
| Auction Construction Ltd | Construction | 2026 |
| Audacia Marketing Labs Ltd | Professional & scientific | 2025 |
| Audere Magno Ltd | Administrative & support | 2024 |
| Audi South West Limited | Wholesale & retail | 2005 |
| Audio Mook Ltd | Professional & scientific | 2019 |
| Audio Visual Sheet Metal Limited | Manufacturing | 2000 |
| Auditquality Consultants Ltd | Professional & scientific | 2018 |
| Augermead Engineering Limited | | 1980 |
| Augment Agency Ltd | Financial services | 2019 |
| Augmented Reality Software Limited | Information & communication | 1991 |
| August Homes Limited | Real estate | 2023 |
| Augusta Corporation Ltd | Wholesale & retail | 2019 |
| Augusta Newham Ltd | Wholesale & retail | 2025 |
| Augustas Carpentry&Joinery Ltd | Construction | 2019 |
| Augustus Family Estates Limited | Real estate | 2021 |
| Aukk Properties Limited | Real estate | 2023 |
| AUM Consulting Ltd | Information & communication | 2010 |
| AUM Empire Limited | Real estate | 2013 |
| AUM Integration Limited | Information & communication | 2018 |
| AUM Technologies Ltd | Information & communication | 2013 |
| AUN Ltd | Health & social care | 2019 |
| Aun's Package Ltd | Real estate | 2021 |
| Aura Beauty MK Ltd | Other services | 2025 |
| Aura Builders Limited | Construction | 2025 |
| Aura Centre of Dental Excellence & Facial Aesthetics Limited | Health & social care | 2014 |
| Aura Consultancy Limited | Professional & scientific | 2025 |
| Aura Direct Limited | Wholesale & retail | 2026 |
| Aura Flooring Limited | Wholesale & retail | 2017 |
| Aura Liberty Care Ltd | Other services | 2021 |
| Aura Liberty Recruitment Ltd | Administrative & support | 2020 |
| Aura Padel Limited | Arts & recreation | 2025 |
| Aura Property Holdings Limited | Real estate | 2017 |
| Aura Shine Ltd | Manufacturing | 2025 |
| Aura Skin Clinic Limited | Health & social care | 2021 |
| Aura Wealth Limited | Construction | 2025 |
| Aurealislume Ltd | Real estate | 2025 |
| Aureate Press Ltd | Information & communication | 2026 |
| Aurelia Interior Staging Ltd | Professional & scientific | 2026 |
| Aurelian Motor Group Ltd | Wholesale & retail | 2025 |
| Aurelux Collectibles Limited | Wholesale & retail | 2025 |
| Aureol Capital Limited | Real estate | 2023 |
| Aureon Property Group Ltd | Real estate | 2025 |
| Aures Consultants Ltd | Professional & scientific | 2018 |
| Aures Investment Limited | Real estate | 2017 |
| Aurigen Medical UK Limited | Professional & scientific | 2022 |
| Auris Restaurant & Lounge Ltd | Hospitality | 2023 |
| Auro Estates Ltd | Real estate | 2019 |
| Aurora Care Ltd | Education | 2025 |
| Aurora Design and Events Ltd | Professional & scientific | 2025 |
| Auroraishika (UK) Writing Instruments Limited | Wholesale & retail | 2012 |
| Aurora’S Workshop Limited | Information & communication | 2025 |
| Austellar Limited | Information & communication | 2013 |
| Austin Bridgeporth Group Ltd | Financial services | 2020 |
| Auszech Limited | Real estate | 2026 |
| Authcite Limited | Information & communication | 2024 |
| Authentic Nigerian MIX Ltd | Manufacturing | 2024 |
| Authentic Shine Ltd | Administrative & support | 2020 |
| Authentic Shine Services Ltd | Administrative & support | 2024 |
| Auto Car Milton Keynes Limited | Wholesale & retail | 2025 |
| Auto Car Trades Ltd | Wholesale & retail | 2025 |
| Auto Claims Fleet Services Limited | Administrative & support | 2011 |
| Auto Classica Storage Limited | Other services | 2017 |
| Auto Focus Ltd | Wholesale & retail | 2020 |
| Auto Globe Heating and Plumbing Limited | Construction | 2024 |
| Auto Globe Ltd | Administrative & support | 2016 |
| Auto IQ Limited | Wholesale & retail | 2014 |
| Auto Motive Pumps Holdings Limited | Other services | 2014 |
| Auto Planet Ltd | Wholesale & retail | 2016 |
| Auto Profile Limited | Manufacturing | 2006 |
| Auto Sowa Ltd | Wholesale & retail | 2020 |
| Auto Spot MK Ltd | Wholesale & retail | 2025 |
| Auto-Stable Motormovers Limited | Transport & logistics | 2018 |
| Autoapps Global Ltd | Information & communication | 2012 |
| Autobody Aesthetics Limited | Wholesale & retail | 2025 |
| Autobot AI Ltd | Information & communication | 2026 |
| Autoclean Europe Limited | Administrative & support | 2003 |
| Autocroft Holdings Limited | Financial services | 2022 |
| Autofonder (UK & Ireland ) Ltd | Wholesale & retail | 2026 |
| Autogap Ltd | Real estate | 2017 |
| Autographica Events Limited | Information & communication | 2014 |
| Autologic Holdings Limited | Financial services | 2018 |
| Autologic Systems Limited | Information & communication | 1993 |
| AUTOM8ED Cloud Ltd | Information & communication | 2021 |
| Automaster (Milton Keynes) Limited | Other services | 2009 |
| Automate Electrical Ltd | Manufacturing | 2019 |
| Automated Paint Technologies Ltd | Manufacturing | 2019 |