| Archgate Scaffolding Solutions Limited | Construction | 2016 |
| Archguild Limited | Real estate | 2008 |
| Architect London Limited | Professional & scientific | 2020 |
| Architectural Design London Ltd | Professional & scientific | 2015 |
| Architecture FAB Ltd | Professional & scientific | 2001 |
| Archmay Ltd | Professional & scientific | 2007 |
| Archugo Property Investment Ltd | Real estate | 2020 |
| Archugo Strategy Ltd | Professional & scientific | 2018 |
| Arcoplan Ltd | Construction | 2018 |
| Arctic Bear Ltd | Information & communication | 2016 |
| Arctic Marmot Ltd | Information & communication | 2016 |
| Arctic Rentals Ltd | Information & communication | 2023 |
| Arctic ZOO Ltd | Information & communication | 2023 |
| Arcus Search Limited | Administrative & support | 2016 |
| Ardennes Investments Limited | Real estate | 2002 |
| Ardfenaig Consulting Limited | Professional & scientific | 2016 |
| Ardsan Limited | Administrative & support | 2026 |
| ARE Developments Limited | Construction | 2010 |
| ARE Property Investments Ltd | Financial services | 2014 |
| Arena Design Ltd | Professional & scientific | 2013 |
| Arete Movement Limited | Information & communication | 2018 |
| Argun Holding Limited | Real estate | 2025 |
| Argutus Limited | Administrative & support | 2015 |
| Argyll Finance Company Limited | Real estate | 1954 |
| ARH Productions Limited | Information & communication | 2018 |
| Arhmiro Ltd | Professional & scientific | 2004 |
| Aria Construction Services Ltd | Administrative & support | 2017 |
| Aria Labs Ltd | Information & communication | 2025 |
| Aria Universal Ltd | Education | 2024 |
| Aries Digital Marketing Consultancy Ltd | Professional & scientific | 2024 |
| Arima Leisure Limited | Construction | 1995 |
| Arima NO.9 Limited | Real estate | 2016 |
| Arima Properties Limited | Households | 1993 |
| Arimas Ltd | Wholesale & retail | 2013 |
| Arioli Limited | Wholesale & retail | 2021 |
| Arixa Health Limited | Information & communication | 2026 |
| ARJ Business Ltd | Real estate | 2022 |
| ARK Group Network Ltd | Construction | 2017 |
| Arkadia Energy Solutions Limited | Construction | 2019 |
| Arkan Property Holdings Ltd | Real estate | 2026 |
| Arkcorse Investments Limited | Real estate | 1958 |
| Arkd Group Limited | Construction | 2019 |
| Arkdtrade Limited | Real estate | 2026 |
| Arkin & Co Limited | Professional & scientific | 2008 |
| Arkin (2004) Limited | Real estate | 2004 |
| Arkley (South West) Limited | Real estate | 2022 |
| Arkley Barnet LLP | | 2024 |
| Arkley Car Wash Ltd | Other services | 2024 |
| Arkley Hand Car Wash Ltd | Wholesale & retail | 2017 |
| Arkley Heating Ltd | Construction | 2017 |
| Arkley Wood Consulting Limited | Professional & scientific | 2025 |
| Arks Consulting Limited | Professional & scientific | 2011 |
| ARL Property Management Limited | Construction | 2010 |
| Arlington Residential HTP1 Limited | Real estate | 2022 |
| Arlington Residential HTP2 Limited | Real estate | 2023 |
| Arlington Residential HTP3 Limited | Real estate | 2024 |
| Arlington Residential HTP4 Limited | Real estate | 2026 |
| Armi Construction Ltd | Construction | 2021 |
| Armks Properties Ltd | Real estate | 2020 |
| Armour (Insurance Services) Limited | Financial services | 1961 |
| Armour K9 Limited | Administrative & support | 2004 |
| Arnco Capital Ltd | Financial services | 2022 |
| Aromatic Coffee Roasters Ltd | Manufacturing | 2025 |
| Aron Marcus Oral Health Care Limited | Health & social care | 2020 |
| ARR9 Limited | Administrative & support | 2026 |
| Arribal Limited | Wholesale & retail | 2012 |
| Arrm Properties and Investments Ltd | Real estate | 2022 |
| Arrow London Builders Ltd | Construction | 2012 |
| Arrow UK Property Limited | Real estate | 2020 |
| ARROW10 Ltd | Construction | 2018 |
| Arsenio Lima Coaching Ltd | Arts & recreation | 2022 |
| Art Build Construction Ltd | Construction | 2023 |
| Art Mosaic Company Limited | Administrative & support | 2008 |
| Artemiris Holdings Ltd | Financial services | 2022 |
| Artificialintelligence.Marketing Ltd | Information & communication | 2025 |
| Artillery Properties Limited | Construction | 1998 |
| Artisans Table Ltd | Hospitality | 2026 |
| Arts & Management International LLP | | 2009 |
| Artudata Ltd | Information & communication | 2017 |
| Arventure Associates Ltd | Information & communication | 2015 |
| Arvik Limited | Real estate | 2017 |
| Arvina Homes Ltd | Real estate | 2021 |
| ARX Cyber Ltd | Professional & scientific | 2020 |
| AS Above, SO Below LDN Ltd | Hospitality | 2019 |
| AS Accountancy Services Ltd | Professional & scientific | 2022 |
| AS EAT Ltd | Hospitality | 2026 |
| AS Energy Ltd | Professional & scientific | 2025 |
| AS Luxe Ltd | Wholesale & retail | 2026 |
| AS Property London Limited | Real estate | 2017 |
| AS Resourcing Limited | Professional & scientific | 2013 |
| ASA Capital Limited | Real estate | 2014 |
| ASA Care Home Limited | Health & social care | 2021 |
| ASA Care Limited | Administrative & support | 2004 |
| ASA Holdco Limited | Financial services | 2018 |
| ASA Propco 1 Limited | Real estate | 2018 |
| ASA Propco 2 Limited | Real estate | 2019 |
| ASA Propco Limited | Real estate | 2018 |
| ASA SPV Limited | Real estate | 2024 |
| ASA Sussex Limited | Financial services | 2021 |
| Asap Professionals Limited | Administrative & support | 2010 |