| Atrushi Properties Ltd | Real estate | 2023 |
| ATS Care Ltd | Health & social care | 2026 |
| ATS Health & Safety Ltd | Administrative & support | 2024 |
| Atsecurity Limited | Administrative & support | 2020 |
| Atsj Ltd | Other services | 2020 |
| ATT Consulting and Systems Integration Ltd | Information & communication | 2017 |
| Attachment Services UK Ltd | Wholesale & retail | 2024 |
| Attah's Limited | Administrative & support | 2019 |
| Attain WSS Global Holdings Limited | Manufacturing | 2018 |
| Attenborough Properties Ltd | Real estate | 2017 |
| Attentech Limited | Wholesale & retail | 2023 |
| Attercliffe Waterside Ltd | Real estate | 2020 |
| Attest Group Ltd | Professional & scientific | 2023 |
| Attest Partners Limited | Professional & scientific | 2025 |
| Attic in Bloom Limited Liability Partnership | | 2023 |
| Atticus Awards Ltd | Wholesale & retail | 2018 |
| Atticus Solutions Limited | Administrative & support | 2003 |
| Attigo CIC | Professional & scientific | 2016 |
| Attis Credit Solutions Limited | Professional & scientific | 2020 |
| Attis Group Limited | Extraterritorial | 2020 |
| Attis Insurance Brokers Ltd | Financial services | 2020 |
| Attis Northern Limited | Financial services | 2021 |
| Attis Sport Limited | Extraterritorial | 2021 |
| Attitude Ltd | Health & social care | 1997 |
| Atul Software Consultants Ltd | Information & communication | 2012 |
| ATW & CT Developments Ltd | Real estate | 2021 |
| ATW Management Company Ltd | Professional & scientific | 2024 |
| ATW Property 1 Ltd | Real estate | 2018 |
| ATW Property 4 Ltd | Real estate | 2019 |
| ATW Property Flips Ltd | Real estate | 2020 |
| ATW Short Stays Ltd | Real estate | 2019 |
| Atypical Studio Ltd | Information & communication | 2017 |
| ATZ Ltd | Wholesale & retail | 2025 |
| AU Holdings Group Ltd | Financial services | 2026 |
| AU Services Ltd | Mining & quarrying | 2015 |
| Aubergine Communications Limited | Information & communication | 2015 |
| Aubergine Insight Limited | Professional & scientific | 2021 |
| Aubrey B Limited | Other services | 2021 |
| Auburn HR Ltd | Administrative & support | 2017 |
| AUC Property Management Limited | Real estate | 2024 |
| AUCT1ON Limited | Wholesale & retail | 2023 |
| Auction Experience Limited | Administrative & support | 2019 |
| Auction Services Limited | Other services | 2020 |
| Auction Vault Limited | Wholesale & retail | 2025 |
| Auctus Edge Ltd | Professional & scientific | 2024 |
| Aucuparia Farming Limited | Agriculture & fishing | 2024 |
| Audacia Consulting Limited | Information & communication | 2007 |
| Audacia Jewellery Limited | Wholesale & retail | 2024 |
| Audatex (UK) Limited | Information & communication | 1986 |
| Audby Lane Management Company Limited | Households | 1995 |
| Audience Collective Limited | Professional & scientific | 2016 |
| Audio Flow AI Ltd | Information & communication | 2025 |
| Audio Mart Limited | Wholesale & retail | 2024 |
| Audio-Technica Limited | Wholesale & retail | 1978 |
| Audioaudioaudio Ltd | Information & communication | 2023 |
| Audiobox Limited | Professional & scientific | 2015 |
| Audiofit Limited | Wholesale & retail | 2012 |
| Audiohub Ltd | Public administration | 2024 |
| Audiology Limited | Other services | 2004 |
| Audit Technologies Ltd | Information & communication | 2026 |
| Auditsu Ltd | Information & communication | 2023 |
| Audots Limited | Information & communication | 2024 |
| Audreams Homes Ltd | Real estate | 2026 |
| Auger Bore Investments Limited | Administrative & support | 2022 |
| Augill Castle Antiques Limited | | 1968 |
| Augmented HR Limited | Professional & scientific | 2019 |
| August Leadership Limited | Administrative & support | 2020 |
| Augusta Midco Limited | Financial services | 2020 |
| Augusta Topco Limited | Financial services | 2020 |
| Augustus Healthcare Limited | Health & social care | 2019 |
| AUK Realisations 2024 Limited | Wholesale & retail | 1973 |
| Auker Rhodes Accounting Limited | Professional & scientific | 2010 |
| Auksánō Ltd | Other services | 2024 |
| Aulis Property Ltd | Other services | 2019 |
| AUM Solutions Limited | Information & communication | 2010 |
| Aumas Trading & Logistics Limited | Wholesale & retail | 2025 |
| Aumkara Yorkshire Limited | Construction | 2023 |
| Aunt Minnie Courses Limited | Education | 2013 |
| Aunty Pheby Foods Limited | Wholesale & retail | 2026 |
| Auocha Ltd | Real estate | 2025 |
| Aura (Newcastle) Holding Company Limited | Professional & scientific | 2007 |
| Aura (Newcastle) Holding Company Phase 2 Ltd | Construction | 2009 |
| Aura (Newcastle) Project Company Limited | Construction | 2007 |
| Aura (Newcastle) Project Company Phase 2 Ltd | Professional & scientific | 2009 |
| Aura Bulk Holdings Ltd | Wholesale & retail | 2026 |
| Aura Content Studios Ltd | Information & communication | 2026 |
| Aura DC Limited | Financial services | 2015 |
| Aura Deals Ltd | Wholesale & retail | 2025 |
| Aura Dental Studio Limited | Health & social care | 2023 |
| Aura Design & Consultancy Limited | Professional & scientific | 2024 |
| Aura Holdings (Newcastle) Limited | Professional & scientific | 2006 |
| Aura Lounge Leeds Ltd | Hospitality | 2026 |
| Aura Marketplace Ltd | Professional & scientific | 2025 |
| Aura Mgmt Limited | Administrative & support | 2024 |
| Aura Paye Limited | Administrative & support | 2023 |
| Aura Realty Developments Ltd | Real estate | 2024 |
| Auraedge Ltd | Wholesale & retail | 2024 |
| Aurangzeb Khalid Holdings Ltd | Financial services | 2025 |
| Aurecharm Ltd | Wholesale & retail | 2025 |
| Aurelius Health Limited | Health & social care | 2024 |