| Askham Park Management Company Limited | Administrative & support | 2014 |
| Askham Storage and Logistics Ltd | Transport & logistics | 2022 |
| Askham Technical Limited | Professional & scientific | 2017 |
| Askham Woof Ltd | Other services | 2019 |
| Askj Investments Ltd | Real estate | 2022 |
| ASL Holdings Bristol Ltd | Administrative & support | 2017 |
| Aslan UK Properties Limited | Real estate | 2019 |
| ASM Joinery Ltd | Construction | 2019 |
| ASN Insight Ltd | Professional & scientific | 2026 |
| Asov Engineering Services Limited | Professional & scientific | 2017 |
| ASP Engineering Services Ltd | Real estate | 2019 |
| ASP Solutions Ltd | Information & communication | 1997 |
| Aspect 4 Limited | Professional & scientific | 2009 |
| Aspect Homes Limited | Extraterritorial | 1964 |
| Aspects Horticultural Services Limited | Other services | 2010 |
| Aspen Housing Limited | Real estate | 2017 |
| Aspinall Entertainments Ltd | Manufacturing | 2024 |
| Aspire Accountancy School Limited | Education | 2016 |
| Aspire Associates Limited | Professional & scientific | 2019 |
| Aspire Learning Consultancy Limited | Information & communication | 2019 |
| Aspiring Enterprises Ltd | Health & social care | 2013 |
| Assault & Battery Limited | Information & communication | 2005 |
| Assent Ltd | Wholesale & retail | 2020 |
| Assetiam Business Consultancy Services Limited | Professional & scientific | 2017 |
| Associated Plastic Services (UK) Limited | Administrative & support | 1998 |
| Associated Recruitment Services Ltd | Administrative & support | 2012 |
| Associated Rediffusion Productions Limited | Information & communication | 1990 |
| Association of Local Environmental Records Centres CIC | Other services | 2009 |
| Assurestaygroup Ltd | Hospitality | 2026 |
| Astbury Formentera Limited | Administrative & support | 1982 |
| Astek Landscapes Limited | Administrative & support | 2011 |
| Astra Business Coaching Limited | Professional & scientific | 2006 |
| Astra Risk and Compliance Ltd | Professional & scientific | 2012 |
| Astral Communications (Wakefield) Limited | Wholesale & retail | 1993 |
| Astro Studio Ltd | Information & communication | 2024 |
| Asubisye Ltd | Health & social care | 2015 |
| Aswda Golden Scissors Ltd | Other services | 2023 |
| AT Pool & TUB Works Ltd | Manufacturing | 2023 |
| AT PR Ltd | Professional & scientific | 2018 |
| ATB Property Services Ltd | Construction | 2010 |
| Atdpaintworkprotection Ltd | Wholesale & retail | 2019 |
| ATE O'Clock Limited | Financial services | 2021 |
| Atelier Home and Garden Limited | Wholesale & retail | 2010 |
| ATG Travel Services Ltd | Extraterritorial | 2025 |
| Atgas Limited | Real estate | 2021 |
| Athelstan Developments Ltd | Construction | 2022 |
| Athena Catering Ltd | Hospitality | 2026 |
| Athena Health, Safety and Well-Being Services Ltd | Education | 2022 |
| Athletic Edge Creative Ltd | Professional & scientific | 2023 |
| Athletic Skills Limited | Other services | 2024 |
| Athletica Health Ltd | Health & social care | 2020 |
| Athley Limited | Hospitality | 2022 |
| Atho Property Ltd | Real estate | 2023 |
| Atiya Spice Takeaway Ltd | Hospitality | 2026 |
| Atkin Business Coaching Limited | Professional & scientific | 2009 |
| Atkin Plumbing Supplies Ltd | Construction | 2025 |
| Atkinson Homes and Developments Ltd | Real estate | 2026 |
| Atkinson Powell Financial Management LLP | | 2010 |
| Atkinson Stanton Limited | Other services | 2008 |
| Atkinson Systems Ltd | Professional & scientific | 2017 |
| Atkinsons Electrical Contracting Services Limited | Construction | 2016 |
| Atlantis One Limited | Extraterritorial | 1973 |
| Atlas Ascend Ltd | Real estate | 2024 |
| Atlas Circuit Solutions Ltd | Professional & scientific | 2026 |
| Atlas Industrial Services Limited | Water & waste | 2002 |
| ATM Group Holdings Limited | Financial services | 2021 |
| ATM Group Services Limited | Financial services | 2019 |
| Atnec Limited | Professional & scientific | 2024 |
| Atom Bars Ltd | Hospitality | 2024 |
| Atoms Consulting Ltd | Professional & scientific | 2019 |
| Atout Clinic Ltd | Health & social care | 2023 |
| ATP (Accounting) Ltd | Professional & scientific | 2017 |
| Atreyu Ventures Limited | Professional & scientific | 2012 |
| Atreyu Vision Limited | Wholesale & retail | 2012 |
| Atrium Accounts Ltd | Professional & scientific | 2011 |
| Atrk Ltd | Real estate | 2020 |
| Attain Productions Ltd | Information & communication | 2019 |
| Attention to Detail Decorating Ltd | Construction | 2022 |
| Attic Attack York Ltd | Construction | 2018 |
| Attic Space Limited | Other services | 2022 |
| Aubergine Ostrich Limited | Wholesale & retail | 2015 |
| Audasi Holdings Limited | Administrative & support | 2007 |
| Audaxe Ltd | Professional & scientific | 2023 |
| Aughton Combined Ltd | Financial services | 2021 |
| Aughton Hall Holdings Limited | Wholesale & retail | 2014 |
| August Ltd | Professional & scientific | 2026 |
| August Mount Recruitment Ltd | Administrative & support | 2024 |
| Augusta Services (Yorkshire) Limited | Financial services | 2018 |
| AUM Wellness Limited | Other services | 2024 |
| Aura Assist - Business Services Limited | Information & communication | 2025 |
| Aura Consulting Services Ltd | Professional & scientific | 2023 |
| Aura Tech Ltd | Professional & scientific | 2023 |
| Aurega Holdings Ltd | Construction | 2010 |
| Aurex Executive Travel Limited | Administrative & support | 2026 |
| Auris Engineering Ltd | Professional & scientific | 2011 |
| Aurora Technical Services Limited | Information & communication | 2026 |
| Ausnom Limited | Professional & scientific | 2004 |
| Austen Ventures Ltd | Wholesale & retail | 2024 |
| Austin Brooks Ltd | Real estate | 2012 |
| Austin Charles Ltd | Other services | 2009 |