| Area Cladding Limited | Construction | 2003 |
| Arefair Limited | Wholesale & retail | 2014 |
| AREFAIRB2B Limited | Wholesale & retail | 2014 |
| Arenty Ltd | Real estate | 2017 |
| Areopagus Media Limited | Information & communication | 2025 |
| Arepa's Station Cambridge Limited | Hospitality | 2019 |
| Arepa's Station Limited | Hospitality | 2016 |
| Ares Management Consulting Ltd. | Professional & scientific | 2018 |
| Ares Trade Co., Ltd | Extraterritorial | 2013 |
| Arete Medical Technologies Ltd | Manufacturing | 2017 |
| Aretelos Ltd | Professional & scientific | 2011 |
| Aretian Capital Limited | Financial services | 2025 |
| Arevat&D Co., Ltd | Manufacturing | 2020 |
| Arfi Business Development Ltd | Professional & scientific | 2024 |
| Argonauts - IT Limited | Information & communication | 2011 |
| Argyle and Henry Street Liverpool (UK) Ltd | Real estate | 2022 |
| Argyle Design Ltd | Professional & scientific | 2003 |
| Argyle Mews Limited | Households | 2010 |
| ARH Brooks Limited | Transport & logistics | 2023 |
| Aricak Painting & Decoration Ltd | Construction | 2021 |
| Aricode Printing Technology Ltd. | Manufacturing | 2017 |
| Arinuk Ltd | Professional & scientific | 2019 |
| Arius Recruit Limited | Administrative & support | 2024 |
| Arjun Estates Limited | Real estate | 2002 |
| ARK Colour Design Limited | Wholesale & retail | 2015 |
| ARK Expeditions Ltd | Administrative & support | 2025 |
| ARK FFF Coaching LLP | | 2025 |
| ARK Home and Garden Limited | Wholesale & retail | 2003 |
| ARK Roofers Ltd | Construction | 2022 |
| ARK Test Labs Ltd | Information & communication | 2016 |
| Arkby Limited | Professional & scientific | 2015 |
| Arkelm Holdings Limited | Professional & scientific | 2016 |
| Arkhill Properties Limited | Real estate | 1985 |
| Arkis Property LET Ltd | Real estate | 2026 |
| Arkley Nursery Landscape Limited | Administrative & support | 2003 |
| Arks Property Ltd | Real estate | 2025 |
| Arla Training Services Ltd | Information & communication | 2013 |
| Arlesey Leisure Ltd | Arts & recreation | 2018 |
| Arley Hill Ventures Limited | Hospitality | 2021 |
| ARM Asia Investment G.P. Limited | Financial services | 2016 |
| ARM Holdings PLC | Financial services | 2018 |
| ARM IP Limited | Information & communication | 2013 |
| ARM Operations Limited | Administrative & support | 2025 |
| ARM Technology Investments 2 Limited | Financial services | 2019 |
| ARM Technology Investments Limited | Financial services | 2014 |
| Arman-Medini Technologies Ltd | Information & communication | 2026 |
| Armandale Trading & Investing Ltd | Professional & scientific | 2026 |
| Armando DE Brito Ltd | Manufacturing | 2023 |
| Armett Construction and Living Solutions Limited | Construction | 2025 |
| Armitage Way Freehold Limited | Households | 2020 |
| Armohi Transport Ltd | Transport & logistics | 2026 |
| Armolio Ltd | Professional & scientific | 2016 |
| Armour Court (Tilehurst) M.C. Limited | Households | 1994 |
| Armstrong Shepherd Associates Limited | Administrative & support | 2013 |
| Arnage Group Ltd | Professional & scientific | 2025 |
| Arnold & Willis Homes Ltd | Real estate | 2026 |
| Arnold Boat Yachts Marine Ltd | Manufacturing | 2024 |
| ARO Piper Trading PVT Ltd | Wholesale & retail | 2017 |
| Aromedia Limited | Administrative & support | 2007 |
| Aromh Hair Limited | Other services | 2023 |
| Aromi Caffe Ltd. | Hospitality | 2012 |
| Aromi Franchise Limited | Administrative & support | 2022 |
| Aron Butler Composites Ltd | Professional & scientific | 2018 |
| ARP Aviation Ltd | Manufacturing | 2025 |
| Arrabona Homes Limited | Real estate | 2022 |
| Arrabona Property Limited | Real estate | 2016 |
| Arredia Limited | Manufacturing | 2025 |
| Arrowhnw Group Ltd | Professional & scientific | 2022 |
| ARS Assets Holdings Ltd | Financial services | 2019 |
| Art & Architecture Limited | Arts & recreation | 2015 |
| Art & Landscape Ltd | Administrative & support | 2003 |
| Art and Culture Education C.I.C. | Wholesale & retail | 2021 |
| Art by Mandy Lowton Ltd | Arts & recreation | 2026 |
| Art for ALL Ltd | Professional & scientific | 2014 |
| Art of Flooring Limited | Construction | 2021 |
| Artaffair Limited | Information & communication | 2003 |
| Artalvia Ltd | Wholesale & retail | 2026 |
| Artchina Limited | Wholesale & retail | 2015 |
| Artdon Lighting Limited | Wholesale & retail | 2024 |
| Artech-It Ltd | Information & communication | 2015 |
| Artechs Labs Ltd | Information & communication | 2014 |
| Artek-Design-House Limited | Professional & scientific | 1996 |
| Artellect Ltd | Education | 2011 |
| Artesis LLP | | 2006 |
| Arthur Court Norman Way Over Management Company Limited | Households | 2017 |
| Arthur Rank Hospice Charity | Health & social care | 2009 |
| Arthur Rank Hospice Limited | Wholesale & retail | 1995 |
| Arthur Rose Limited | Financial services | 2024 |
| Articulate Hrms Consulting Limited | Information & communication | 2010 |
| Artifex-H Ltd | Manufacturing | 2023 |
| Artin Holding Ltd | Financial services | 2025 |
| Artios Pharma Limited | Professional & scientific | 2015 |
| Artiosense Limited | Professional & scientific | 2021 |
| Artisan Electrics (Cambridge) Ltd | Construction | 2018 |
| Artisan Motion Ltd | Professional & scientific | 2024 |
| Artisan of Everything Ltd | Financial services | 2024 |
| Artists in Residency Limited | Information & communication | 2025 |
| Artium Limited | Arts & recreation | 2019 |
| Artium Media Relations Limited | Other services | 2017 |
| Artoai Ltd | Professional & scientific | 2022 |