| ARC Energy Solutions Limited | Construction | 2025 |
| Arc-Gen Hilta Limited | Professional & scientific | 1948 |
| Arc-Gen Limited | Professional & scientific | 1955 |
| Arcfast Limited | Construction | 2023 |
| Archery Fields Management Company Limited | Real estate | 2016 |
| Architectural Project Solutions Limited | Professional & scientific | 2009 |
| Architecture Ventures Limited | Professional & scientific | 2021 |
| Arcway Property Ltd | Real estate | 2024 |
| Ardern Exports Ltd | Wholesale & retail | 2022 |
| Ardingley Court Management Limited | Households | 1986 |
| Area 6 Kings Heath Management Company Limited | Households | 2007 |
| Argo Shrewsbury Ltd | Health & social care | 2026 |
| Argonought Limited | Construction | 2000 |
| Argyll Court RTM Limited | Households | 2010 |
| ARH Group Limited | Construction | 1994 |
| ARH Projects Ltd | Construction | 2025 |
| ARH TH FP Limited | Real estate | 2020 |
| Ariaconsult Limited | Professional & scientific | 2020 |
| Arkbar Developments Limited | Other services | 2021 |
| Arkenfield Stable Hire Ltd | Administrative & support | 2009 |
| ARL Developments Ltd | Real estate | 2013 |
| Arlington Lodge Residents Association Limited | Real estate | 2018 |
| Armitage Road (Rugeley) Management Limited | Other services | 2006 |
| Armstrong Court (Swindon) Management Company Limited | Households | 2002 |
| Armstrong Siddeley Owners Club Limited | Wholesale & retail | 1973 |
| Aron Court Management Company Limited | Households | 2002 |
| Around the Wrekin Developments Ltd | Real estate | 2023 |
| Arrol Green Design Studio Limited | Professional & scientific | 2024 |
| Arrow Court Industrial Estate Limited | Administrative & support | 1998 |
| Arrow Fruit Ltd | Agriculture & fishing | 2025 |
| Arrow Heart Limited | Transport & logistics | 2024 |
| Arrow Property Holdings Limited | Professional & scientific | 2016 |
| Arscott Barns Management Limited | Households | 2008 |
| Arscott Golf Club Limited | Arts & recreation | 2018 |
| Art Illusions Limited | Wholesale & retail | 2015 |
| Art Motors Limited | Wholesale & retail | 2021 |
| Art World Gallery Limited | Wholesale & retail | 2024 |
| Artcadia Limited | Manufacturing | 2018 |
| Arthan Holdings Limited | Professional & scientific | 2014 |
| Artis Vulpa Design Limited | Arts & recreation | 2013 |
| Arty Party Limited | Arts & recreation | 2010 |
| Arundel Limited | Households | 1991 |
| ARV Properties Shropshire Limited | Real estate | 2024 |
| Arvensis Ecology Ltd | Administrative & support | 2015 |
| ARW90 Ltd | Professional & scientific | 2015 |
| Asap Building Contractors Ltd | Construction | 2026 |
| Ascend Technology Solutions Ltd | Information & communication | 2022 |
| Asensei Ltd | Information & communication | 2019 |
| ASH Concept Ltd | Hospitality | 2024 |
| ASH Grove WEM Management Co Limited | Real estate | 2020 |
| Ashanti Empress Limited | Wholesale & retail | 2023 |
| Ashbridge-Law Limited | Information & communication | 2024 |
| Ashby Road Management Company Limited | Households | 2008 |
| Ashkaan DA Vera Limited | Extraterritorial | 2026 |
| Ashley Downing Performance Ltd | Arts & recreation | 2017 |
| Ashmore Grove Management Company Limited | Households | 2023 |
| Ashton & Co Legal Services Limited | Professional & scientific | 2022 |
| Ashton Planning and Development Ltd | Professional & scientific | 2019 |
| Ashtree Trading Group Limited | Financial services | 2019 |
| Ashtree Trading Ltd | Wholesale & retail | 2015 |
| Asian Horizons Ltd | Hospitality | 2022 |
| Asjl Ltd | Real estate | 2024 |
| ASK (GB) Limited | Construction | 2002 |
| Aspect (Greenford) Management Limited | Households | 2007 |
| Aspect Consulting Group Ltd | Administrative & support | 2007 |
| Aspen Grove (Rumney) Residents Management Company Limited | Households | 2021 |
| Aspire Accountancy and Bookkeeping Services Limited | Real estate | 2018 |
| Aspire Bookkeeping Services Limited | Professional & scientific | 2024 |
| Aspirit Consultants Limited | Information & communication | 2020 |
| Asrp Services Limited | Real estate | 2022 |
| Assess Assist Limited | Education | 2014 |
| Asset Solutions (UK) Limited | Real estate | 2010 |
| Asset Accountancy (Shrewsbury) Ltd | Professional & scientific | 2022 |
| Asset Surfacing and Construction Limited | Construction | 2007 |
| Association of British Certification Bodies | Other services | 1996 |
| Assured Equipment Services Limited | Manufacturing | 2018 |
| Astley Brook Management Company Limited | Households | 2014 |
| Aston RD Ltd | Construction | 2023 |
| Astra-Lightsco Limited | Wholesale & retail | 2024 |
| Astraeus Holidays Limited | Administrative & support | 2017 |
| ASW Solutions Ltd | Administrative & support | 2025 |
| AT the Elbow Ltd | Information & communication | 2025 |
| AT360 Ltd | Information & communication | 2017 |
| Atbay Limited | Construction | 2017 |
| Atchams Limited | Real estate | 2019 |
| Atelier Privé Limited | Wholesale & retail | 2025 |
| Athena Exchange Ltd | Real estate | 2023 |
| ATJ Personalised Limited | Professional & scientific | 2017 |
| Atlantis Property Limited | Real estate | 2001 |
| Attainability UK Limited | Wholesale & retail | 2007 |
| Attilough Limited | Real estate | 2026 |
| Attractive Realities Ltd | Information & communication | 2010 |
| Atwer Limited | Administrative & support | 2010 |
| Auctora Limited | Information & communication | 2025 |
| Audlem Software Ltd | Information & communication | 2001 |
| Aura Hairdressing Ltd | Other services | 2010 |
| Aussiedental Ltd | Health & social care | 2021 |
| Austins Window Cleaning Ltd | Administrative & support | 2023 |
| Authentic Evolution Ltd | Other services | 2015 |
| Autism Dadcast Media Ltd | Information & communication | 2026 |