| Authentically ME Ltd | Health & social care | 2020 |
| Authentix Limited | Professional & scientific | 1959 |
| Authentix Services Company Limited | Professional & scientific | 2016 |
| Auto Refinishers York Limited | Wholesale & retail | 2003 |
| Auto Computer Services Limited | Extraterritorial | 1991 |
| Auto Cosmetics of York Ltd | Wholesale & retail | 2012 |
| Auto Diagnostics (York) Ltd | Wholesale & retail | 2008 |
| Auto Flipz UK Ltd | Wholesale & retail | 2025 |
| Auto Motivate Limited | Professional & scientific | 2020 |
| Auto Replace Limited | Extraterritorial | 2013 |
| Auto Services York Ltd | Manufacturing | 2009 |
| Auto Telematics Ltd | Information & communication | 2020 |
| Autoceltic Ltd | Wholesale & retail | 2025 |
| Autogas Services Ltd | Professional & scientific | 2002 |
| Autogrow AI Ltd | Professional & scientific | 2025 |
| Autohaus Diagnostics Limited | Wholesale & retail | 2013 |
| Autohorn Fleet Services Limited | Administrative & support | 1995 |
| Autohorn Group Limited | Administrative & support | 2015 |
| Autohorn Investments Ltd | Administrative & support | 2018 |
| Autohorn Property Services Limited | Transport & logistics | 2016 |
| Automaton Limited | Information & communication | 2016 |
| Automotive Equipment Solutions UK Limited | Wholesale & retail | 2005 |
| Automotive Risk Management Limited | Extraterritorial | 2008 |
| Automotive Solutions (York) Limited | Wholesale & retail | 2015 |
| Automotive Telematics Ltd | Information & communication | 2025 |
| Autovip Sales Ltd | Wholesale & retail | 2016 |
| Autumnvale Financial Services Limited | Real estate | 2004 |
| Autus Lifetime Planning Limited | Financial services | 2013 |
| AV Dental Limited | Health & social care | 2025 |
| Avalon Concepts Limited | Construction | 2007 |
| Avalon Phase 2 Management Company Limited | Households | 2026 |
| Avante Events Ltd | Construction | 2025 |
| Avanti Internet Supplies Limited | Wholesale & retail | 2009 |
| Avanti Product Supplies Limited | Wholesale & retail | 2005 |
| Avanti Renewables Limited | Construction | 2012 |
| AVC (Abergavenny) Limited | Extraterritorial | 2019 |
| AVE -Ryedale Ltd | Real estate | 2021 |
| Avento Daisy Limited | Wholesale & retail | 2025 |
| Aveyard Property Ltd | Real estate | 2025 |
| Avgo- Flaxby Ltd. | Manufacturing | 2022 |
| Avha Living Spaces Ltd | Real estate | 2024 |
| Avian, Wildlife and ZOO Veterinary Services Limited | Professional & scientific | 2023 |
| Aviva (Peak NO.2) UK Limited | Professional & scientific | 1991 |
| Aviva Administration Limited | Administrative & support | 1997 |
| Aviva Client Nominees UK Limited | Extraterritorial | 2003 |
| Aviva Equity Release UK Limited | Financial services | 1996 |
| Aviva Erfa 15 UK Limited | Financial services | 2008 |
| Aviva Investment Solutions UK Limited | Financial services | 2007 |
| Aviva Life & Pensions UK Limited | Financial services | 1996 |
| Aviva Life Holdings UK Limited | Professional & scientific | 1989 |
| Aviva Life Investments International (General Partner) Limited | Financial services | 2009 |
| Aviva Life Investments International (Recovery) Limited | Financial services | 1986 |
| Aviva Life Investments International L.P. | | 2018 |
| Aviva Life Services UK Limited | Administrative & support | 1989 |
| Aviva Management Services UK Limited | Administrative & support | 1970 |
| Aviva Master Trust Trustees UK Limited | Professional & scientific | 2023 |
| Aviva Pension Trustees UK Limited | Financial services | 1989 |
| Aviva Protection UK Limited | Financial services | 2007 |
| Aviva Savings Limited | Financial services | 2002 |
| Aviva Trustees UK Limited | Financial services | 2014 |
| Aviva Uklap De-Risking Limited | Financial services | 1998 |
| Aviva Wealth Holdings UK Limited | Financial services | 2009 |
| Aviva Wrap UK Limited | Administrative & support | 2002 |
| Avon Fields (Durrington) Management Company Limited | Households | 2011 |
| Avondale Estates Limited | Real estate | 2013 |
| Avondale Ventures Ltd | Extraterritorial | 2024 |
| Avorium Limited | Wholesale & retail | 2021 |
| Avro Distribution Limited | Financial services | 2019 |
| Avro Investments | Financial services | 2011 |
| AVS Commercial Limited | Wholesale & retail | 2022 |
| AW Landscapes (York) Ltd | Administrative & support | 2023 |
| AW Pond Supplies and Maintenance Ltd | Wholesale & retail | 2020 |
| Awards in a Box Ltd | Administrative & support | 2025 |
| Awareness Days Ltd | Information & communication | 2017 |
| Awdm Consulting Ltd | Professional & scientific | 2014 |
| Awel Afan (Port Talbot) Management Company Limited | Households | 2022 |
| Awel Y Mynydd (Pembrey) Management Company Ltd | Households | 2023 |
| AWM Survey Equipment Limited | Extraterritorial | 2009 |
| AWT Solutions Ltd | Professional & scientific | 2025 |
| Axaioi Ltd | Information & communication | 2020 |
| Axante Limited | Information & communication | 2013 |
| Axel Motorsport Limited | Manufacturing | 2001 |
| Axiality Limited | Information & communication | 2021 |
| Axiom (York) Limited | Professional & scientific | 2018 |
| Axiom-Planned Vegetation Management Limited | Professional & scientific | 2017 |
| Axis Procurement Services Limited | Professional & scientific | 2023 |
| Axminster & Cambourne Capital Limited | Financial services | 2023 |
| Axup Pipe Supplies Limited | Manufacturing | 2020 |
| AY Radiology Limited | Health & social care | 2022 |
| AY Sannaz Ltd | Wholesale & retail | 2026 |
| Ay-Pe Ltd | Information & communication | 2008 |
| Ayaz Lara Ltd | Hospitality | 2022 |
| Aylesham Village Phase 2B and 2C (Aylesham) Residents Management Company Limited | Households | 2023 |
| Aytoun Consulting Limited | Professional & scientific | 2002 |
| AZ UK Real Estate Ltd | Administrative & support | 2007 |
| AZ Valves (UK) Limited | Wholesale & retail | 1992 |
| Azamjaan Holdings Limited | Professional & scientific | 2025 |
| Azania Projects Ltd | Professional & scientific | 2024 |
| Azeem Incorporation Ltd | Wholesale & retail | 2024 |
| Azira Capital Ltd | Professional & scientific | 2025 |