| Artisando Ltd | Hospitality | 2025 |
| Artur Cars Limited | Transport & logistics | 2020 |
| Arulabeauty Ltd | Manufacturing | 2011 |
| ARV Developments Limited | Real estate | 2024 |
| Aryan Property UK Ltd | Financial services | 2022 |
| Arzum Lezzet Limited | Hospitality | 2019 |
| AS Railtech Ltd | Construction | 2023 |
| ASA Legal Ltd | Professional & scientific | 2025 |
| ASA Suppliers Ltd | Wholesale & retail | 2025 |
| Asaké Publishing Limited | Information & communication | 2023 |
| Asalaw Company Limited | Health & social care | 2022 |
| Asalite Limited | Information & communication | 2015 |
| Asanka Flavors Extra Limited | Hospitality | 2024 |
| Asanka Flavors Limited | Hospitality | 2018 |
| Asanka House of Sauces Limited | Hospitality | 2023 |
| Asaph Placement Ltd | Administrative & support | 2025 |
| Ascent Hub Limited | Administrative & support | 2022 |
| Ascent Staffing Solutions Ltd | Administrative & support | 2024 |
| ASD Renewables Limited | Energy | 2019 |
| Asemed Limited | Health & social care | 2026 |
| Asfitness Studio Ltd | Arts & recreation | 2023 |
| Asha the Hope Services Ltd | Construction | 2009 |
| Ashanti Divine Rental Hub Limited | Arts & recreation | 2025 |
| Asher Property Limited | Real estate | 2024 |
| Ashikka Consultancy Ltd | Professional & scientific | 2023 |
| Ashley Conlan Mortgages Ltd | Financial services | 2020 |
| Ashton Industrial Sales Limited | Manufacturing | 1982 |
| ASI Decorators Ltd | Construction | 2023 |
| Asia Bistro Limited | Hospitality | 2025 |
| Asier Limited | Real estate | 2020 |
| ASK Compliance Ltd | Professional & scientific | 2025 |
| ASK Security Ltd | Administrative & support | 2019 |
| Askcyber Limited | Information & communication | 2020 |
| Askew Road Mansions Management Company Limited | Households | 2007 |
| ASL Aspire Support Learn CIC | Administrative & support | 2017 |
| ASL Living Ltd | Health & social care | 2025 |
| Aslan Cafe Ltd | Hospitality | 2019 |
| Aslan I.D Properties Ltd | Real estate | 2025 |
| Asoc Consulting Limited | Information & communication | 2025 |
| Aspects Investments Ltd | Financial services | 2019 |
| Aspire-Gt Limited | Professional & scientific | 2011 |
| Aspiring Horizons Ltd | Education | 2024 |
| ASQ Accountants Limited | Professional & scientific | 2019 |
| Assa Commercial Ltd | Professional & scientific | 2024 |
| Asset Pharma Resources Limited | Administrative & support | 2009 |
| Associated Independent Merchant Stockists Limited | Wholesale & retail | 1982 |
| Associated Tapchangers Limited | Manufacturing | 2013 |
| Association of Nigerian Social Workers United Kingdom C.I.C. | Health & social care | 2021 |
| Assured Electrical & Automation Ltd | Construction | 2026 |
| Assured IT Group Ltd | Information & communication | 2026 |
| Assured Security Limited | Administrative & support | 1983 |
| Astarcapital Ltd | Administrative & support | 2022 |
| Astarcare Ltd | Health & social care | 2019 |
| Aston Tool & Pressings Limited | Manufacturing | 1948 |
| Aston Vale Estate Management Company Limited | Households | 2013 |
| Astor House Limited | Households | 1998 |
| Astro Donuts Ltd | Wholesale & retail | 2025 |
| Astro Lighting (Asia) Limited | Wholesale & retail | 2016 |
| Astro Lighting (China) Limited | Manufacturing | 2015 |
| Astro Lighting (Europe) Limited | Manufacturing | 2015 |
| Astro Lighting (USA) Limited | Wholesale & retail | 2015 |
| Astro Lighting Holdings Limited | Wholesale & retail | 2015 |
| Astro Lighting Limited | Wholesale & retail | 1997 |
| Astute Technology Ltd | Professional & scientific | 2008 |
| AT Home Support Services Limited | Administrative & support | 2015 |
| AT Last Free CIC | Information & communication | 2023 |
| AT Salvage Ltd | Wholesale & retail | 2026 |
| At-Gas, Heating & Maintenance Ltd | Construction | 2023 |
| At.Components Ltd | Manufacturing | 2022 |
| Ates Grill Ltd | Hospitality | 2025 |
| ATG Brickwork Ltd | Construction | 2023 |
| Athelstan House Freehold Co Ltd | Professional & scientific | 2023 |
| Athelstan House Management Limited | Households | 1985 |
| Athena-Hygieia Limited | Health & social care | 2024 |
| Atiba Music Limited | Information & communication | 2024 |
| Atisa Concepts Limited | Real estate | 2022 |
| Atkinson Property Holdings Limited | Households | 2022 |
| Atlantic Gate Consulting Limited | Wholesale & retail | 2013 |
| Atlantic Gate Healthcare Solutions Limited | Administrative & support | 2018 |
| Atlantis Food Ltd | Wholesale & retail | 2020 |
| Atlas ICS Limited | Wholesale & retail | 2017 |
| Atlas Medicare Ltd | Health & social care | 2021 |
| Atlas Valve International Ltd | Wholesale & retail | 2024 |
| Atol Insulation Ltd | Construction | 2020 |
| Atoll Services Ltd | Construction | 2015 |
| ATP Roofing Solutions Ltd | Construction | 2025 |
| Atstek Ltd | Information & communication | 2013 |
| Attachy UK Ltd | Construction | 2020 |
| Attentive Care Ltd | Health & social care | 2013 |
| Attune Psychotherapy Limited | Health & social care | 2023 |
| Atwell Roofing and Building Ltd | Construction | 2026 |
| AU Tax Advisory Ltd | Professional & scientific | 2025 |
| Audio Grooves Ltd | Administrative & support | 2024 |
| Audio Logic Limited | Administrative & support | 2004 |
| Augite Limited | Information & communication | 2021 |
| August Partners UK Ltd | Real estate | 2022 |
| Aunty Rachel Community Interest Company | Health & social care | 2025 |
| Aura & Aroma Ltd | Wholesale & retail | 2025 |
| Aura Regulatory Ltd | Administrative & support | 2016 |
| Aurelencia Ltd | Wholesale & retail | 2025 |