| 3MAC Systems Limited | Stockport | 2016 |
| 3MAN Security Limited | Cheshunt | 2024 |
| 3MD Technical Recruitment Ltd | Norwich | 2015 |
| 3MEGOS Limited | Llanrwst | 2018 |
| 3ML Tax Solutions Limited | Bough Beech | 2009 |
| 3MS Maintenance Limited | Truro | 2015 |
| 3MS Solutions Services Limited | Manchester | 2022 |
| 3N Consultancy & Services Ltd | London | 2018 |
| 3NESS Ltd | Barking | 2006 |
| 3NINETEEN Limited | Ware | 2020 |
| 3NRGY Limited | Rotherham | 2024 |
| 3NTT International Limited | Ilford | 2013 |
| 3NV Group Services Limited | Leigh-On-Sea | 2026 |
| 3NVISION Limited | Leigh On Sea | 2020 |
| 3P Consult Ltd | Pencoed, Bridgend | 2010 |
| 3P Consultancy Services Limited | Warrington | 2025 |
| 3P Innovation Trustee Limited | Warwick | 2020 |
| 3P Procure Limited | Stockton On Tees | 2026 |
| 3P Protection Limited | Accrington | 2013 |
| 3P Webquery Limited | London | 2025 |
| 3PEAT Projects Limited | Horley | 2015 |
| 3PH Group Ltd | London | 2017 |
| 3PHASE Recruitment Limited | Potters Bar | 2018 |
| 3PI Financial Services Ltd | Mayfair | 2016 |
| 3PILLRS Ltd | Aberdeen | 2018 |
| 3PL Management Limited | Kingston Upon Thames | 2013 |
| 3PL Resources Limited | Croydon | 2021 |
| 3PLE H Security Limited | Hounslow | 2024 |
| 3PLS Platform Limited | Amersham | 2023 |
| 3PLUS International Ltd | Purley | 2011 |
| 3PLWOW Ltd | Blyth | 2016 |
| 3PN Group Ltd | London | 2021 |
| 3POINT Recruitment Group Ltd | Lancing | 2025 |
| 3PPP Ltd | Macclesfield | 2013 |
| 3PS Group Limited | Gosport | 2019 |
| 3PS Marketing Limited | Dawlish | 2013 |
| 3PX Recruitment Limited | London | 2013 |
| 3R Consortium Limited | Barnet | 2003 |
| 3R Global Talent Ltd | Birmingham | 2024 |
| 3R Group Systems Ltd | Bolton | 2019 |
| 3R Restoration Ltd | Rotherhithe New Road | 2021 |
| 3R Secure Services Ltd | London | 2024 |
| 3R Softwash Limited | Lanark | 2018 |
| 3R Strategy Limited | London | 2014 |
| 3R Technology Head Company Limited | Preston | 2021 |
| 3RD Career Ltd | Swindon | 2025 |
| 3RD Generation Tattoos Limited | Batley | 2010 |
| 3RD I Solution Ltd | Widnes | 2018 |
| 3RD Momentum Limited | Aberdeen | 2019 |
| 3RD November Limited | Hounslow | 2012 |
| 3RD Space Consulting Limited | Harrogate | 2015 |
| 3RD Storm Limited | Stockport | 2018 |
| 3RDEYE Systems Limited | Walsall | 2006 |
| 3REPUBLIC Campers Ltd | Nuneaton | 2025 |
| 3RG Maritime Security Ltd | Poole | 2011 |
| 3S Aberdeen Ltd | Westhill | 2020 |
| 3S Home Cleaning Services Ltd | Harrow | 2024 |
| 3S Services Limited | London | 2015 |
| 3S Trading Group Ltd | Newcastle Upon Tyne | 2026 |
| 3S Travel Ltd | Ilford | 2022 |
| 3S-AUTOMATION Limited | | 2007 |
| 3S-HAI Travels Limited | Leicester | 2010 |
| 3SC Scaffolding Hire & Sales Ltd | Weymouth | 2019 |
| 3SEARCH Limited | Cheltenham | 2014 |
| 3SES Security Ltd | Bushey | 2023 |
| 3SIX5 (UK) Limited | Lutterworth | 2012 |
| 3SIXTY Beauty Limited | Lincoln | 2026 |
| 3SIXTY Consulting (UK) Limited | Bristol | 2006 |
| 3SIXTY Global Limited | Oxford | 2009 |
| 3SIXTY Inventories Limited | London | 2019 |
| 3SIXTY Management Limited | Bristol | 2006 |
| 3SIXTY Private & Commercial Property Solutions Ltd | London | 2025 |
| 3SIXTY Protect Ltd | London | 2015 |
| 3SIXTY Resourcing Ltd | Peterborough | 2018 |
| 3SIXTY Talent Management Ltd | Northampton | 2018 |
| 3SIXTY Transfers Limited | Manchester | 2024 |
| 3SM Landscaping Limited | Dudley | 2025 |
| 3STEPSAHEAD Ltd | Woodgate Chichester | 2025 |
| 3T Services Limited | Cheshire | 2002 |
| 3T Connect Limited | Christchurch | 2024 |
| 3T Enermech Limited | Aberdeen | 2022 |
| 3T Global Bidco PLC | Dorset | 2024 |
| 3T Global Holdco Limited | Hurn | 2017 |
| 3T Global Midco 2 Limited | Hurn, Dorset | 2026 |
| 3T Global Midco Limited | Hurn | 2023 |
| 3T Global Subco Limited | Hurn | 2017 |
| 3T Group Ltd | Enfield | 2016 |
| 3T Training Solutions Limited | Hurn | 2023 |
| 3T Transform Limited | Hurn | 2023 |
| 3T Travel & Tourism Limited | Barking | 2011 |
| 3T Workforce Solutions Limited | Hurn | 2023 |
| 3TB Limited | London | 2025 |
| 3TECH Rope Access Ltd | Moffat | 2018 |
| 3TEES Investment Limited | London | 2019 |
| 3TEN Holdings Limited | Havant | 2015 |
| 3TM Group Ltd | London | 2023 |
| 3TW Investments Limited | Horsham | 2011 |
| 3V3 UK Herts Ltd | Harpenden | 2025 |
| 3VB Services Limited | East Grinstead | 2017 |
| 3VEA Ltd | Sevenoaks | 2025 |