| Arla Maintenance Ltd | Construction | 2020 |
| Arleb Limited | Financial services | 2016 |
| Arley Estates Limited | Administrative & support | 2008 |
| Arlington Court Management Company Limited | Real estate | 1982 |
| Arlos Adventures Dog Care Ltd | Other services | 2024 |
| Arlos Castles and Softplay Ltd | Arts & recreation | 2026 |
| ARM Electrix Ltd | Construction | 2013 |
| ARM Networks Limited | Information & communication | 2016 |
| ARM Properties Enterprise Ltd | Real estate | 2025 |
| Armadillo Services Ltd | Extraterritorial | 2015 |
| Armistead Ltd | Information & communication | 2003 |
| Armstrong Global Ltd | Transport & logistics | 2012 |
| Armstrong Global Yachts Ltd | Administrative & support | 2025 |
| Armstrong Pictures Limited | Information & communication | 2008 |
| Armstrong Property Services Ltd | Administrative & support | 2023 |
| Armstrong Residential Ltd | Real estate | 2025 |
| Armstrong Rigg Planning Limited | Professional & scientific | 2012 |
| ARN Property Ltd | Real estate | 2023 |
| ARO Heli Services Ltd | Manufacturing | 2024 |
| Arokka Group Ltd | Professional & scientific | 2026 |
| Arora and Arora Limited | Professional & scientific | 2020 |
| Arora Inc Ltd | Real estate | 2026 |
| Arora Limited | Real estate | 2015 |
| Arora Properties Group Ltd | Real estate | 2025 |
| Arora Property Services Ltd | Real estate | 2025 |
| Aroundu Ltd | Information & communication | 2025 |
| Arpora Holding Limited | Financial services | 2026 |
| Arpora Limited | Administrative & support | 2026 |
| Arpora Trading Limited | Administrative & support | 2009 |
| Arrc Studio Limited | Information & communication | 2025 |
| Arrkac Limited | Wholesale & retail | 2023 |
| Arrow Electronics (UK) Limited Partnership | | 1997 |
| Arsin Ltd | Transport & logistics | 2016 |
| Art Frame & Mount Bespoke Picture Framing Limited | Manufacturing | 2018 |
| Art in Logistic Ltd | Construction | 2023 |
| Art Nail & Beauty Ltd | Other services | 2026 |
| Artculture Studios Limited | Information & communication | 2025 |
| Artemisian Limited | Arts & recreation | 2018 |
| Artha Consultancy Ltd | Professional & scientific | 2021 |
| Articulata Limited | Professional & scientific | 2021 |
| Artis Video Limited | Information & communication | 2024 |
| Artisan Bespoke Builders Limited | Construction | 2010 |
| Artist Agency Ltd | Arts & recreation | 2020 |
| Artistry Properties Limited | Real estate | 2016 |
| Artiz Transport Consultancy Ltd | Professional & scientific | 2022 |
| Arts Property Limited | Real estate | 2020 |
| Artsermon Ltd | Health & social care | 2009 |
| Arulandu Ltd | Professional & scientific | 2019 |
| Arundel Gardens (Bromham) Limited | Households | 2013 |
| Arundel Smith Churchill Properties Limited | Real estate | 2000 |
| Arvinder Singh Ltd | Construction | 2015 |
| ARZ Foods Ltd | Hospitality | 2025 |
| AS & AA Property Investments Ltd | Real estate | 2023 |
| AS Active Solutions Global Limited | Professional & scientific | 2023 |
| AS Consultancy Ltd | Professional & scientific | 2024 |
| AS Intelligence Ltd | Information & communication | 2024 |
| AS Pump Solutions Ltd | Construction | 2023 |
| ASA Mahal Ltd | Real estate | 2019 |
| ASA Medicals Ltd | Health & social care | 2011 |
| Asabiyyahgroup Ltd | Health & social care | 2024 |
| Asad MED Ltd | Health & social care | 2026 |
| Asami Corporation Limited | Administrative & support | 2017 |
| Asante Services Limited | Wholesale & retail | 2025 |
| Asbury Heating Maintenance Limited | Construction | 1986 |
| Ascenda Property Group Ltd | Real estate | 2025 |
| Ascendant Multimedia Ltd | Wholesale & retail | 2026 |
| Ascendant Recruitment Limited | Administrative & support | 2002 |
| Ascension Recruitment Ltd | Administrative & support | 2022 |
| Ascentia Property Group Ltd | Construction | 2024 |
| Ascentium Associates Limited | Education | 2012 |
| Asdem Investments Ltd | Real estate | 2026 |
| Asds Propertys Limited | Real estate | 2021 |
| Aseeda Limited | Wholesale & retail | 2024 |
| Asep Services Limited | Manufacturing | 2019 |
| ASF Energy Limited | Professional & scientific | 2020 |
| ASG (Arlesey) Ltd | Wholesale & retail | 2018 |
| ASH Homes Development Herts Ltd | Construction | 2025 |
| ASH Prime Services Ltd | Administrative & support | 2026 |
| Ashburmag Limited | Households | 2017 |
| Ashcroft Investments Limited | Real estate | 2012 |
| Ashfell Limited | Information & communication | 2025 |
| Ashfield Property Services Ltd | Professional & scientific | 2022 |
| Ashgl Ltd | Manufacturing | 2025 |
| Ashhab Food Ltd | Hospitality | 2025 |
| Ashi Shah Properties Ltd | Real estate | 2021 |
| Ashington Rogers Limited | Real estate | 2017 |
| Ashley Builders Limited | Construction | 2009 |
| Ashley Lambe Coiffeur Ltd | Other services | 2022 |
| Ashridge Cliff Properties Limited | Construction | 2003 |
| Ashvale Haulage Limited | Transport & logistics | 2001 |
| Ashway Expertise Ltd | Professional & scientific | 2012 |
| Ashwell Contracts Limited | Construction | 2000 |
| Ashwith Properties Ltd | Real estate | 2024 |
| Ashwood Tree Care & Landscapes Ltd | Administrative & support | 2026 |
| ASJ Riding School Limited | Other services | 2024 |
| ASK Europe Holdings Limited | Professional & scientific | 2025 |
| ASK Europe Limited | Professional & scientific | 1994 |
| ASK Opticians Ltd | Professional & scientific | 2017 |
| ASK Scientific Consulting Ltd | Professional & scientific | 2020 |
| ASK Skin Beauty Ltd | Other services | 2021 |