| Atherston Holdings Ltd | Birmingham | 2025 |
| Atherstone Care Services Ltd | Birmingham | 2026 |
| Atherstone Pharma Ltd | Atherstone | 2012 |
| Atherton Medical & Legal Ltd | Bristol | 2019 |
| Atherton Neuropsychology Consultancy Ltd | Sheffield | 2021 |
| Atherton Physiotherapy and Sports Injury Clinic Limited | Manchester | 2019 |
| Atherton Therapeutic Services Limited | Wigan | 2025 |
| Athesham Limited | Walsall | 2024 |
| Athi-Sihle Limited | Nottingham | 2016 |
| Athiaa Ltd | Rotherham | 2022 |
| Athina Medical Limited | Wrexham | 2013 |
| Athis Endo Ltd | Bury St. Edmunds | 2020 |
| Athkar Medical Ltd | Winchester | 2015 |
| Athlete 17 Limited | Northampton | 2020 |
| Athlete Matters Limited | Manchester | 2008 |
| Athlete Recovery Management Ltd. | Bicester | 2016 |
| Athlete SOS Ltd | Elgin | 2025 |
| Athletes Foundry Ltd. | Barnard Castle | 2019 |
| Athletes Inbalance Ltd | Henley-On-Thames | 2020 |
| Athletes Journey Home UK Ltd | Bristol | 2024 |
| Athletes' Angels Ltd | Aberfeldy | 2006 |
| Athletes' Performance UK Limited | London | 2013 |
| Athletic Approach Limited | Northampton | 2023 |
| Athletic Health Ltd | London | 2016 |
| Athletic Performance & Therapy Ltd | Portsmouth | 2026 |
| Athletic Performance Club Ltd | Oxford | 2024 |
| Athletica Health Ltd | York | 2020 |
| Athleticare Systems Limited | Cambridge | 2024 |
| Athleticode Ltd | Midhurst | 2026 |
| Athleva Limited | Worcester Park | 2024 |
| Athlevo Ltd | Nottingham | 2025 |
| Athma Life Sciences Ltd | Rochester | 2023 |
| Athnan Limited | Hayes | 2008 |
| Athol Thomson Sports Podiatry Limited | Hillsborough | 2023 |
| Atholl Health Ltd | Grimsby | 2015 |
| Athom Healthcare Solution Limited | Leeds | 2024 |
| Athome Care Group Ltd | Weston Super Mare | 2022 |
| Athomes Group UK Ltd | Derby | 2024 |
| Athona Doctors Limited | Romford | 2011 |
| Athona Health Limited | Romford | 2011 |
| Athona Research Ltd | Sheffield | 2025 |
| Athorpe Health Care Limited | London | 2001 |
| Athos Physio Limited | Manchester | 2020 |
| Athraa Limited | Bristol | 2011 |
| Athree Spa London Ltd | Coleford | 2012 |
| Athro Tayler Limited | Cheltenham | 2015 |
| Athzaar Limited | Wilmslow | 2024 |
| ATI2UDE Care Limited | Newport | 2025 |
| Atiase Rehabilitation Care Limited | Surrey | 2020 |
| Atiba Galaxy Ltd | Romford | 2013 |
| Atienza Ltd | Hull | 2026 |
| Atif Consultants Limited | Birmingham | 2013 |
| Atigrac Limited | Gravesend | 2023 |
| Atijulya Care Limited | Manchester | 2022 |
| Atikos Care Ltd | London | 2025 |
| Atikos Ltd | London | 2022 |
| Atilola Adeleke Healthcare Services Limited | Essex | 2025 |
| Atim Consultancy Limited | Ipswich | 2022 |
| Atimaz Homes Ltd | Greenhithe | 2026 |
| ATIME4CHANGE Ltd | Northampton | 2025 |
| Atinuke Limited | Dagenham | 2021 |
| Atipa Healthcare Group Ltd | Stoke-On-Trent | 2014 |
| Atipica Ltd | Barnet | 2026 |
| Atiq Care Solutions Limited | Leatherhead | 2014 |
| Atiqs Solutions Ltd | Ashton-Under-Lyne | 2023 |
| Atique Healthcare Ltd | Preston | 2026 |
| Atitoks Limited | Enfield | 2014 |
| Ativar Consulting Ltd | Norwich | 2024 |
| Ativas Medical Ltd | Harrow | 2022 |
| Atiya Healthcare Services Limited | Derby | 2010 |
| Atiya Ateeq Art Psychotherapy Ltd | London | 2026 |
| ATJ Healthcare Limited | Bridgend | 2021 |
| ATJ Ortho Limited | Glasgow Central | 2025 |
| Atjk Locum Ltd | Luton | 2021 |
| ATK Business Associates Limited | London | 2020 |
| Atkin Marine Limited | Edinburgh | 2020 |
| Atkingells Ltd | Bracknell | 2012 |
| Atkins Care Ltd | Croydon | 2025 |
| Atkins Care Services Limited | Walton-On-Thames | 2007 |
| Atkins Health & Performance Ltd | Evesham | 2025 |
| Atkins Physiotherapy Consultants Limited | Woodford Green | 2015 |
| Atkinson & OOI Ltd | Chippenham | 2017 |
| Atkinson Chiropractic Limited | Penryn | 2003 |
| Atkinson Consulting Services Limited | Doncaster | 2021 |
| Atkinson Medical Consulting Ltd | Pinner | 2010 |
| Atkinson Medical Limited | Stevenage | 2026 |
| Atkinson Morley's Hospital Neurosciences Research Foundation(The) | Cranmer Terrace Tooting | 1983 |
| Atkinson-Reader Healthcare Limited | Newcastle Upon Tyne | 2025 |
| Atkinsonadhdcare Ltd | Nottinghamshire | 2025 |
| Atlanta Healthcare Limited | Norwich | 2004 |
| Atlanthor Ltd | Ilford | 2022 |
| Atlantic Care Limited | London | 2018 |
| Atlantic Clinic Ltd | Southampton | 2013 |
| Atlantic Dental Limited | Salisbury | 2012 |
| Atlantic Enterprise U.K. Limited | Bournemouth | 1992 |
| Atlantic Forest Conservation CIC | Bristol | 2025 |
| Atlantic Fostering Services Ltd | Ilford | 2024 |
| Atlantic Globe Limited | London | 2016 |
| Atlantic Healthcare Services Limited | Ilford | 2023 |
| Atlantic Home Eyecare Limited | Barnstaple | 2017 |