| Armoise Limited | Professional & scientific | 2018 |
| Arms of Grace | Other services | 2010 |
| Arna Genext Solutions Limited | Health & social care | 2024 |
| Aroha Services Ltd | Hospitality | 2026 |
| Aroma Business PVT Limited | Hospitality | 2018 |
| Arora's Group Limited | Information & communication | 2020 |
| Arova Consulting Limited | Information & communication | 2026 |
| ARQA51 Ltd | Information & communication | 2015 |
| ARR Riyadh Limited | Health & social care | 2016 |
| Arras Trading Limited | Wholesale & retail | 2026 |
| Arrow Real Estate Limited | Real estate | 2019 |
| Arslan's Fashionfrenzy Limited | Wholesale & retail | 2025 |
| Art and Brand Advisory Ltd | Professional & scientific | 2019 |
| Art Dynamics Limited | Information & communication | 2009 |
| Art in Herts Community Interest Company | Wholesale & retail | 2023 |
| Artbeat Hub Ltd | Wholesale & retail | 2026 |
| Artecs Group LLP | | 2024 |
| Artecs International Limited | Wholesale & retail | 2003 |
| Arterial Technology Limited | Information & communication | 2022 |
| Arterial Vascular Engineering UK Limited | Professional & scientific | 1995 |
| Artha Nexus Limited | Construction | 2025 |
| Arthavista Ltd | Wholesale & retail | 2025 |
| Artheo Ltd | Construction | 2019 |
| Arthur Holloway Consulting Ltd | Professional & scientific | 2019 |
| Arthur Victor Ltd | Information & communication | 2008 |
| Articad Holdings Limited | Financial services | 2004 |
| Articad Limited | Information & communication | 1992 |
| Artichoke Ventures Limited | Professional & scientific | 2026 |
| Artident Limited | Manufacturing | 2025 |
| Artimusdigital Ltd | Professional & scientific | 2016 |
| Artmed Healthcare Limited | Health & social care | 2012 |
| Artria London Limited | Education | 2012 |
| Artur Kapusta Ltd | Transport & logistics | 2025 |
| Arvin Management Services Ltd | Real estate | 2021 |
| Arvo Systems Ltd | Information & communication | 2026 |
| Arwens Contracts Ltd | Construction | 2018 |
| Arwens Decorating Ltd | Construction | 2018 |
| Arwens Limited | Construction | 2006 |
| Arya Construction Ltd | Construction | 2025 |
| Arya T Catering Ltd | Hospitality | 2026 |
| Aryaa Care Limited | Real estate | 2015 |
| Aryan IT Solutions Limited | Information & communication | 2014 |
| Arzo Services Limited | Real estate | 2026 |
| AS Consultancy Direct Services Ltd | Information & communication | 2024 |
| AS First Solutions Ltd | Construction | 2023 |
| AS Investments Limited | Professional & scientific | 2011 |
| AS London Construction Ltd | Construction | 2026 |
| AS One (Watford) Ltd | Administrative & support | 2020 |
| AS Plumbing Ltd | Construction | 2015 |
| As&Ams General Property Maintenance Ltd | Administrative & support | 2026 |
| AS24 Fuel Card Ltd | Wholesale & retail | 1985 |
| Asa-Nyo Consultancy Services Ltd | Professional & scientific | 2025 |
| Asahi Investment Ltd | Financial services | 2024 |
| Asanteman Watford CIC | Education | 2025 |
| Asao Limited | Administrative & support | 2022 |
| Asap Assets Limited | Real estate | 2015 |
| Asap Property Management Ltd | Real estate | 2026 |
| ASB Direct Limited | Wholesale & retail | 2013 |
| ASB Freight International Ltd | Transport & logistics | 2024 |
| ASB Renovations Ltd | Construction | 2024 |
| Ascad Ltd | Manufacturing | 2025 |
| Ascending Heights Ltd | Health & social care | 2025 |
| Ascension Training Ground Ltd | Arts & recreation | 2025 |
| Ascom Systems Ltd | Information & communication | 2010 |
| Ascot Build Group Ltd | Construction | 2026 |
| Ascot Court Residents Company Limited | Households | 1999 |
| Ascot Edge Management Ltd | Households | 2015 |
| Ascot International Consulting Ltd | Professional & scientific | 2024 |
| Asecoo Ltd | Administrative & support | 2025 |
| ASG Tax Consultants UK Ltd | Professional & scientific | 2010 |
| ASG Wellness Being Ltd | Administrative & support | 2014 |
| ASH Properties Investments Ltd | Real estate | 2022 |
| Ashan Limited | Real estate | 2018 |
| Ashbee Investment Limited | Real estate | 2022 |
| Ashbee JV Limited | Real estate | 2022 |
| Ashbee Property Limited | Financial services | 2022 |
| Ashby Enterprises Ltd | Financial services | 2019 |
| Ashendon Recruitment Limited | Administrative & support | 1999 |
| Ashendorf & Associates Limited | Real estate | 2005 |
| Asheridge Grove (Chesham) Management Company Limited | Households | 2016 |
| Ashgood Classic and Sportscars Limited | Wholesale & retail | 2013 |
| Ashh Property Ltd | Real estate | 2025 |
| Ashigari Limited | Financial services | 2014 |
| Ashiq Motors Ltd | Wholesale & retail | 2023 |
| Ashish Chandra Limited | Professional & scientific | 2017 |
| Ashleaf Limited | Other services | 1986 |
| Ashleigh Construction International Ltd. | Construction | 2023 |
| Ashleigh Property Advisory Ltd. | Real estate | 2024 |
| Ashleigh Property Consultants Ltd | Real estate | 2021 |
| Ashleigh Property Management Ltd | Real estate | 2024 |
| Ashley John Mitchell Ltd | Construction | 2008 |
| Ashlong Developments Limited | Construction | 2006 |
| Ashok Driving Academy Ltd | Education | 2014 |
| Ashray Ltd | Real estate | 2025 |
| Ashridge Osteopathy Limited | Health & social care | 2025 |
| Ashruta Property Ltd | Real estate | 2025 |
| Ashtavinayak Associates (UK) Ltd | Administrative & support | 2013 |
| Ashtavinayak Pharma Ltd | Professional & scientific | 2026 |
| Ashton Union Limited | Real estate | 2022 |
| Ashwell Place Residents Company Limited | Real estate | 2006 |