| Astro Housing Ltd | Real estate | 2015 |
| Astron Holdings and Investments Limited | Real estate | 2016 |
| Astute Media Limited | Information & communication | 2003 |
| Astute Metrics Limited | Administrative & support | 2001 |
| ASW Paving & Construction Ltd | Construction | 2019 |
| AT on Line Computing Limited | Information & communication | 1993 |
| AT the Woods Limited | Hospitality | 2023 |
| Atchak Ltd | Professional & scientific | 2026 |
| Atelier Build Ltd | Professional & scientific | 2012 |
| ATG Access Ltd | Manufacturing | 1991 |
| Atgm Plumbing and Heating Solutions Ltd | Construction | 2025 |
| Athena Bridal Jewellery Limited | Wholesale & retail | 2019 |
| Atherstone Myers Limited | Professional & scientific | 2021 |
| Athlone Extrusions (U.K.) Limited | Administrative & support | 1984 |
| Athos Business Solutions Limited | Professional & scientific | 2005 |
| Athos Cloud Accounting Limited | Professional & scientific | 2018 |
| Atif&Bilal Ltd | Wholesale & retail | 2025 |
| Atlas Alpha Company Ltd | Real estate | 2022 |
| Atlas Building Products Ltd | Wholesale & retail | 2025 |
| Atlas Imaging Ltd | Health & social care | 2025 |
| Atlas Incorporated | Professional & scientific | 2020 |
| Atlas Seven Ltd | Wholesale & retail | 2024 |
| Atman Consultancy Ltd | Information & communication | 2011 |
| Atom EYE Ltd | Health & social care | 2015 |
| Atomic Engineering Holdings Limited | Financial services | 2012 |
| Atomy Global Care Centre Ltd | Other services | 2023 |
| Atos JIU Jitsu UK Kids Ltd | Education | 2024 |
| Atos Shop UK Ltd | Wholesale & retail | 2020 |
| ATS Brands Ltd | Administrative & support | 2024 |
| ATS Premier Groups Limited | Real estate | 2020 |
| ATT Tuning UK Ltd | Wholesale & retail | 2021 |
| Attenger Ltd | Professional & scientific | 2017 |
| Atthi Consultancy Ltd | Health & social care | 2013 |
| Attracting Real Leverage Limited | Information & communication | 2011 |
| Attwood Engineering Consultancy Ltd | Professional & scientific | 2018 |
| Atwalls Ltd | Real estate | 2018 |
| Atwals & Dhesi Ltd | Real estate | 2018 |
| Atwals Estate Ltd | Real estate | 2017 |
| Auchlunkart Hospitality Management UK Limited | Hospitality | 2024 |
| Audhali Capital Group Ltd | Wholesale & retail | 2017 |
| Audible & Visual Security Limited | Other services | 1989 |
| Audio Visual Specialist Limited | Construction | 2019 |
| Audrey & Wolf Ltd | Wholesale & retail | 2020 |
| Augmen Property Investments Limited | Real estate | 2018 |
| Augument IT Solutions Limited | Information & communication | 2019 |
| AUM Housing Ltd | Construction | 2025 |
| Auntee Care Community Interest Company | Health & social care | 2025 |
| Aura Clarity Ltd | Wholesale & retail | 2023 |
| Aurajewel Property Management Limited | Households | 2001 |
| Aurameir Creative Ltd. | Information & communication | 2015 |
| Aurisella London Ltd | Wholesale & retail | 2025 |
| Aurora Electrics Ltd | Construction | 2022 |
| Aurora Land and Developments Limited | Real estate | 1999 |
| Aurum Homes Management Ltd | Real estate | 2010 |
| Aurum Housing CIC | Real estate | 2020 |
| Autism Assessors Ltd | Health & social care | 2021 |
| Auto Commerce Limited | Wholesale & retail | 2022 |
| Auto Illuminate Limited | Construction | 2025 |
| Autochive Limited | Information & communication | 2026 |
| Autoera Ltd | Wholesale & retail | 2019 |
| Autograph Executives Ltd | Transport & logistics | 2021 |
| Autograph Weddings Ltd | Professional & scientific | 2014 |
| Automate Anything Limited | Information & communication | 2020 |
| Automate Global Ltd | Extraterritorial | 2023 |
| Automate International Ltd | Wholesale & retail | 2022 |
| Automatemyreports Limited | Information & communication | 2021 |
| Automotive Consultancy Services Ltd | Professional & scientific | 2024 |
| Automotive Safety Consultancy Ltd | Professional & scientific | 2012 |
| Automotive Upgrades Ltd | Wholesale & retail | 2022 |
| Autosan Limited | Manufacturing | 1993 |
| Autoscratchuk Limited | Wholesale & retail | 2012 |
| Autumn Days (Tamworth) Ltd | Other services | 2009 |
| Autumn Leaflet Distribution Limited | Extraterritorial | 2018 |
| AV Enterprise Ltd | Real estate | 2023 |
| AV Fears Limited | Administrative & support | 2025 |
| AV Futures Ltd | Real estate | 2025 |
| AV Mech Ltd | Manufacturing | 2023 |
| Avalanche Capital Limited | Financial services | 2015 |
| Avalanche Development Services Limited | Financial services | 2015 |
| Avalon Technology Group LLP | | 2019 |
| Avance Consulting Limited | Professional & scientific | 2009 |
| Avania Group Limited | Real estate | 2026 |
| Avant Property Maintenance Limited | Construction | 2025 |
| Avant Property Solutions Ltd | Real estate | 2024 |
| Avanti Housing CIC | Real estate | 2019 |
| Avaro Developments Ltd | Real estate | 2020 |
| Avatar Advice Limited | Real estate | 2002 |
| Avenira Estates Limited | Real estate | 2003 |
| Aventus Coaching Ltd | Education | 2018 |
| Avenue Platform & Access Ltd | Construction | 2019 |
| Avern Recruitment Ltd | Administrative & support | 2025 |
| Avers Consultancy Ltd | Other services | 2019 |
| Aviast Ltd. | Education | 2012 |
| Avis Infotech Limited | Information & communication | 2012 |
| AVN Property Ltd | Real estate | 2017 |
| Avon 4 Ltd | Real estate | 2023 |
| Avon BP Ltd | Real estate | 2021 |
| Avon Heights Property Management Ltd | Households | 2020 |
| Avon Homes Limited | Construction | 2013 |
| Avon Homes Private Clients Limited | Construction | 2022 |