| ACT 4 Services Limited | Camberwell | 2015 |
| ACT 6 Limited | London | 2023 |
| ACT Associates Limited | Stourbridge | 1991 |
| ACT Awareness Limited | Northampton | 2024 |
| ACT Build Change Ltd | Skipton | 2019 |
| ACT Coaching and Training Limited | Redditch | 2025 |
| ACT Conveyance Tracking Limited | Hailsham | 2025 |
| ACT Creative Ltd. | Helpston | 2012 |
| ACT Digital Consulting Ltd | London | 2025 |
| ACT Digital Ltd | Sale | 2014 |
| ACT for Hope Ltd | London | 2025 |
| ACT Happy Ltd | Newport | 2024 |
| ACT II Scene VII Films Ltd | Leeds | 2018 |
| ACT III Ltd | Hove | 2023 |
| ACT Informatics Limited | Bideford | 2024 |
| ACT Insurance Systems Limited | Warndon | 1992 |
| ACT IT Solutions Ltd | Crawley | 2023 |
| ACT Normal Ltd | Henley-On-Thames | 2023 |
| ACT of GOD Ltd | Bromley | 2023 |
| ACT on Energy | Alcester | 1998 |
| ACT on This - the TV Actors’ Network Ltd | Mediacityuk | 2010 |
| ACT OUT Ltd | Wednesbury | 2014 |
| ACT Property Services Ltd | Cobham | 2010 |
| ACT Seven Technology Limited | Southampton | 2008 |
| ACT Systems Limited | Chesterfield | 2013 |
| ACT the Fool Ltd | London | 2024 |
| ACT Trader Technologies Ltd | North Harrow | 2022 |
| ACT Training Services | London | 2006 |
| ACT Two Scene One Productions Ltd | Edinburgh | 2023 |
| ACT With Meraki Ltd | London | 2026 |
| ACT! Software Limited | Newcastle Upon Tyne | 2013 |
| Act-On Software Limited | London | 2013 |
| Act-Uk Ltd | Broadstone | 2021 |
| ACT7 Ltd | Blackpool | 2026 |
| Acta 201 Ltd | Manchester | 2015 |
| Acta Consulting Limited | Bournemouth | 2024 |
| Acta Data Ltd | Ellesmere Port | 2022 |
| Acta Edge Limited | Liverpool | 2026 |
| Acta Enterprises Limited | Dagenham | 2025 |
| Acta Labs Ltd | London | 2026 |
| Actaeon Information Systems Ltd | Surrey | 1998 |
| Actaeus Ltd | London | 2025 |
| Actalink Limited | Poole | 2025 |
| Actant Limited | London | 2000 |
| Actawin Ltd | Solihull | 2017 |
| Actcon Ltd | London | 2024 |
| Actdesign (UK) Ltd | Newcastle Upon Tyne | 2014 |
| Actdev Ltd | Broxbourne | 2022 |
| Actdrive Technology Limited | Colchester | 2000 |
| Acte Prealable Limited | London | 2011 |
| Acteamity Limited | West Malling | 2025 |
| Actec Projects Limited | Ringwood | 2016 |
| Actechivate Software Ltd | Stamford | 2026 |
| Actef Ltd | Benfleet | 2022 |
| Actek Consulting Ltd | London | 2015 |
| Actelligent (Scotland) Company Limited | Edinburgh | 2018 |
| Actelligent (U.K.) Company Limited | London | 2018 |
| Actevo Limited | London | 2020 |
| Actgreennow Ltd | Feltham | 2022 |
| Acthentic Ltd | London | 2026 |
| Actian Europe Limited | London | 2005 |
| Actibility Limited | London | 2017 |
| Actibux Ltd | Reading | 2026 |
| Actica Consulting Limited | Guildford | 1997 |
| Actica Holdings Limited | Guildford | 2009 |
| Actie Limited | Worthing | 2026 |
| Actifinder Ltd | Richmond Upon Thames | 2021 |
| Actiitalk Limited | Walsall | 2021 |
| Actimage Ltd | London | 2019 |
| Actimates Limited | Greenford | 2024 |
| Actimize UK Limited | Southampton | 2004 |
| Actin Web Marketing Limited | Bournemouth | 2015 |
| Acting Office Limited | London | 2022 |
| Acting on a Dream Limited | Wandsworth | 2014 |
| Acting PAL Ltd | London | 2024 |
| Acting UP Limited | Edinburgh | 2000 |
| Actinides IT Centre Ltd | London | 2022 |
| Actinium Media Ltd | Enfield | 2012 |
| Actiom Ltd. | London | 2008 |
| Action 365 Ltd | Manchester | 1999 |
| Action and Motion Ltd | Croydon | 2025 |
| Action Arriving Ltd | London | 2018 |
| Action B Ltd | Reading | 2019 |
| Action BI Ltd | Exeter | 2015 |
| Action Boats Ltd | Reading | 2026 |
| Action Broadcast Company Ltd | Redhill | 2000 |
| Action Cars Limited | Harrow | 1991 |
| Action Circuits (U.K.) Limited | Luton | 1987 |
| Action Computers Ltd | Camden | 2019 |
| Action Computing Limited | Tring | 2019 |
| Action Dashboards Limited | Solihull | 2023 |
| Action Dating Ltd | London | 2024 |
| Action Designs Ltd | Billericay | 2017 |
| Action Economy Ltd | Bradford | 2026 |
| Action Factory Publishing Limited | Skelmersdale | 2020 |
| Action Festival Holdings Limited | Harrow | 2022 |
| Action for Carers (Oxfordshire) Ltd | Abingdon | 2012 |
| Action for People CIC | Mildenhall | 2015 |
| Action Force Entertainment Limited | London | 2024 |
| Action Fraud One Limited | London | 2026 |