| ARK Professional Services Limited | Professional & scientific | 1999 |
| Arkham Films Limited | Information & communication | 2025 |
| Armatool Distributors Limited | Wholesale & retail | 1991 |
| Arnold Advice Limited | Financial services | 2021 |
| Arnsoft Limited | Information & communication | 2018 |
| Aroma Herts Ltd | Hospitality | 2021 |
| Aroma Lounge Hatfield Ltd | Hospitality | 2025 |
| Arram Business Solutions Ltd | Information & communication | 2018 |
| Arribo Ltd | Transport & logistics | 2025 |
| Arrow Investments (UK) Limited | Real estate | 2010 |
| Arsam Properties Ltd | Real estate | 2025 |
| Artificial Properties Ltd | Real estate | 2023 |
| Artisan Chocolaterie Ltd | Hospitality | 2012 |
| Artisan Naturals Limited | Manufacturing | 2025 |
| ARX Solutions Limited | Manufacturing | 2008 |
| ASA Stringhoppers Ltd | Manufacturing | 2018 |
| Asbestech Limited | Water & waste | 1997 |
| Ascend Life Coaching Ltd | Health & social care | 2018 |
| Ascentra Group Ltd | Financial services | 2025 |
| Ascentra Strategy Ltd | Information & communication | 2025 |
| Asha Technologies Limited | Construction | 2016 |
| Ashbrittle Limited | Administrative & support | 2014 |
| Ashbys Services Limited | Manufacturing | 2004 |
| Ashley Court Freehold Limited | Real estate | 2015 |
| Ashokan Engineering Consultancy Ltd | Information & communication | 2026 |
| Ashurst Electrical Contractors Ltd | Construction | 2015 |
| Ashwitha Ltd | Information & communication | 2026 |
| Asia Nails and Beauty Supply Ltd | Wholesale & retail | 2018 |
| ASK 4 Eco Limited | Wholesale & retail | 2010 |
| Aski-Green Holdings Limited | Financial services | 2022 |
| ASP Plumbing and Heating Services Limited | Construction | 2016 |
| Aspects Roofing Solutions Ltd | Construction | 2025 |
| Aspen Education & Migration Solutions Ltd | Professional & scientific | 2024 |
| Aspen Security Consultants Limited | Administrative & support | 2012 |
| Aspern Gate Limited | Professional & scientific | 2003 |
| Aspire Consultancy (CHB) Limited | Administrative & support | 2017 |
| Aspire Knowledge Ltd | Education | 2025 |
| Aspire Property Consultants Limited | Real estate | 2021 |
| Aspire-Gb Ltd | Wholesale & retail | 2017 |
| Aspirees Ltd | Professional & scientific | 2025 |
| Aspiro Edtech Limited | Information & communication | 2025 |
| Asset Growth Management Ltd | Wholesale & retail | 2016 |
| Assign-It Limited | Information & communication | 2001 |
| Associated Decorators (ST Albans) Limited | Construction | 2008 |
| Associated Decorators Limited | Construction | 2008 |
| Assor London Ltd | Transport & logistics | 2019 |
| Aston Executive Ltd | Transport & logistics | 2025 |
| Aston Knights Construction Ltd | Construction | 2024 |
| Astoria Global Ltd | Wholesale & retail | 2024 |
| Astra Projects Applications & Consulting (Apac) Ltd | Information & communication | 2016 |
| Astra Telecommunications Limited | Information & communication | 2009 |
| Astrobrands Ltd | Wholesale & retail | 2024 |
| Astrobrands Wholesale Limited | Wholesale & retail | 2025 |
| AT Developement Limited | Real estate | 2022 |
| Ataroma Ltd | Hospitality | 2022 |
| ATH Cleaning Limited | Administrative & support | 2025 |
| ATH Property Services Ltd | Construction | 2017 |
| Athlete Grid Ltd | Information & communication | 2026 |
| Atlantic Accounting & Taxation Services Limited | Professional & scientific | 2011 |
| Atlas Clinic Ltd | Health & social care | 2025 |
| Atlas Learn Ltd | Education | 2026 |
| Atta Morning DEW Limited | Transport & logistics | 2026 |
| Attentive Education Ltd | Education | 2023 |
| Attila Cleaning Ltd | Administrative & support | 2019 |
| Attimore Properties Ltd | Hospitality | 2024 |
| Attosh Holdings Limited | Financial services | 2025 |
| Attosh Limited | Hospitality | 2023 |
| Attuned to Children Limited | Health & social care | 2023 |
| Atyn Limited | Real estate | 2023 |
| AU Security Ltd | Administrative & support | 2021 |
| Audacity Platform Limited | Real estate | 2017 |
| Auditaxes International LLP | | 2014 |
| Aura Shisha Lounge Ltd | Wholesale & retail | 2026 |
| Auris Protection Limited | Wholesale & retail | 2021 |
| Aurixia Ltd | Hospitality | 2018 |
| Auto Cars & Parts Ltd | Wholesale & retail | 2019 |
| Auto Mobike Experts Ltd | Wholesale & retail | 2025 |
| Auto Mobile Experts Ltd | Wholesale & retail | 2025 |
| Auto Scripts Integration Limited | Information & communication | 2021 |
| Autoline Management Services Limited | Wholesale & retail | 2014 |
| Autosedge Ltd | Wholesale & retail | 2025 |
| AV C&A Ltd | Construction | 2012 |
| AVA Properties Management Ltd | Real estate | 2024 |
| Avanza Holdings Ltd | Administrative & support | 2025 |
| Avanza Ltd | Information & communication | 2016 |
| Avenue Tennis Limited | Arts & recreation | 2015 |
| Avera Retail Limited | Wholesale & retail | 2023 |
| Averee Ltd | Education | 2010 |
| Averis Technologies Ltd | Information & communication | 2025 |
| Avery Home Improvements Limited | Administrative & support | 2008 |
| Avery Home Solutions Ltd | Construction | 2015 |
| Avisan Limited | Administrative & support | 2022 |
| Avlets Holdings Ltd | Extraterritorial | 2023 |
| AVP Bravo Limited | Hospitality | 2025 |
| Avsa Healthcare Services Limited | Health & social care | 2016 |
| Avsk Logistics Ltd | Transport & logistics | 2025 |
| AW Edits Ltd | Professional & scientific | 2024 |
| Awan Reliance Ltd | Transport & logistics | 2023 |
| Awesome Peri Peri Ltd | Hospitality | 2025 |
| Awoe Enterprises Limited | Administrative & support | 2016 |