| Aquasomnus Limited | Health & social care | 2010 |
| Aquatic Dietetics Ltd | Wholesale & retail | 2023 |
| Aquatic Installation & Maintenance Limited | Construction | 2019 |
| Aquatrace Limited | Construction | 2026 |
| Aquavita Pools Ltd | Construction | 2024 |
| Aquex Ltd | Construction | 2026 |
| Aquila (Nacton) Limited | Administrative & support | 2010 |
| Aquila 1516 Limited | Extraterritorial | 2009 |
| Aquila BTE 1 Limited | Extraterritorial | 2007 |
| Aquila BTE 2 Limited | Real estate | 2007 |
| Aquila Chelmsford Limited | Extraterritorial | 2001 |
| Aquila Developments Limited | Construction | 2001 |
| Aquila EHS Limited | Real estate | 2002 |
| Aquila Estates Limited | Real estate | 2002 |
| Aquila Finance Limited | Financial services | 2014 |
| Aquila House Holdings Limited | Financial services | 2001 |
| Aquila House Property Limited | Financial services | 2011 |
| Aquila Instruments Limited | Other services | 2000 |
| Aquila Investment Property Holdings Limited | Financial services | 2014 |
| Aquila Investment Property Limited | Financial services | 2014 |
| Aquila Ipswich Limited | Extraterritorial | 2018 |
| Aquila Maldon Limited | Extraterritorial | 2007 |
| Aquila Management LLP | | 2012 |
| Aquila Open Space Limited | Extraterritorial | 2006 |
| Aquila PM Limited | Real estate | 2018 |
| Aquila Real Estate Consulting Limited | Real estate | 2025 |
| Aquila Real Estate Limited | Real estate | 2002 |
| Aquila TL Limited | Real estate | 2018 |
| AR Investment Management Limited | Professional & scientific | 2011 |
| AR Plumbing & Heating (Chelmsford) Ltd | Construction | 2021 |
| AR Service Group Ltd | Administrative & support | 2026 |
| Arabian Musk London Limited | Manufacturing | 2023 |
| Aran Recruitment Ltd | Construction | 2012 |
| Arba Ltd | Construction | 2022 |
| Arbour Finance Consulting Ltd | Professional & scientific | 2018 |
| Arbuthnot YON C&I Limited | Professional & scientific | 2024 |
| Arbuthnot YON FS Limited | Professional & scientific | 2024 |
| Arbuthnot YON Ltd | Administrative & support | 2014 |
| ARC Parfums Ltd | Manufacturing | 2026 |
| Arcady Architecture Limited | Professional & scientific | 2020 |
| Arcav Ltd | Real estate | 2025 |
| Archers Plumbing & Heating Solutions Limited | Construction | 2014 |
| Architectural Graphics Design Associates Limited | Professional & scientific | 2023 |
| Archoak Properties Limited | Real estate | 2000 |
| Arcis Limited | Information & communication | 2025 |
| Arco Property Investment Ltd | Real estate | 2020 |
| Arcole Labs Limited | Information & communication | 2025 |
| Arcsense Solutions Ltd | Information & communication | 2025 |
| Arctic Traders Limited | Wholesale & retail | 1993 |
| Ardamy Limited | Construction | 2022 |
| Ardanza Limited | Professional & scientific | 2016 |
| Ardent Space Systems Ltd | Professional & scientific | 2026 |
| Ardenvale (Chelmsford) Management Company Limited | Households | 1982 |
| Arderne Management Services Limited | Professional & scientific | 2020 |
| Ardian Outdoor Limited | Construction | 2014 |
| Area 515 Fitness Limited | Arts & recreation | 2017 |
| Ares Partners Limited | Professional & scientific | 2020 |
| Ares Services Ltd | Administrative & support | 2022 |
| Argentic Europe Limited | Financial services | 2026 |
| Argon 18 Investments Limited | Real estate | 2024 |
| Argyle E-Sales Ltd | Wholesale & retail | 2025 |
| Aria Newbury Park Residents Association Limited | Households | 2005 |
| Ariel Bidco Limited | Financial services | 2026 |
| Ariel Midco Limited | Financial services | 2026 |
| Ariel Topco Limited | Financial services | 2026 |
| Arisdale Property Leasing Company Limited | Real estate | 2003 |
| ARK Holdings (West Yorkshire) Limited | Manufacturing | 2023 |
| ARK Precision Engineering Limited | Manufacturing | 1998 |
| Arkaan Limited | Hospitality | 2014 |
| Arkadius Logistics Ltd | Transport & logistics | 2018 |
| Arkferos Limited | Information & communication | 2024 |
| Arkley Soil Investigation LLP | | 2015 |
| Arlo King Property & Investment Limited | Real estate | 2020 |
| Arlo Piper Limited | Administrative & support | 2024 |
| Armbow Limited | Real estate | 2017 |
| Armchair IT Limited | Information & communication | 2007 |
| Armour Group Land Sea Air Limited | Financial services | 2013 |
| Armour House Development Group Limited | Construction | 1947 |
| Armour Roofing Services Ltd | Construction | 2008 |
| Armour Shutters Ltd | Administrative & support | 2005 |
| Armourend Limited | Construction | 2006 |
| Arna Purna Trekking Ltd | Manufacturing | 2020 |
| Arneg Korea Co Ltd | Wholesale & retail | 2025 |
| Arnii Tech Ltd | Information & communication | 2023 |
| Arnold Grant & Waters Limited | Financial services | 2016 |
| Arnold Grant & Waters NO. 7 Limited | Extraterritorial | 2021 |
| Aroma Beauty Limited | Other services | 2026 |
| Around the World Catering Limited | Hospitality | 2020 |
| Arran IT Limited | Information & communication | 2022 |
| Arrantek Limited | Information & communication | 2016 |
| Array Electrics Ltd | Construction | 2015 |
| Arroka Consulting Ltd | Professional & scientific | 2021 |
| Arrow Security Systems Limited | Administrative & support | 2013 |
| ARS Tech Solutions Ltd | Information & communication | 2025 |
| Art Aesthetics Clinic Ltd | Wholesale & retail | 2023 |
| Art Carpentry & Building Limited | Construction | 2023 |
| Art in Music Ltd | Other services | 2016 |
| Art Skin Clinic Limited | Other services | 2022 |
| Artbuild Development Ltd | Construction | 2022 |
| Arthur Anthony Interiors Ltd | Construction | 2013 |