| 3 M'S Timberframe & Carpentry Limited | Llanelli | 2009 |
| 3 Merchant Square (Nominee) Limited | London | 2006 |
| 3 Mice Limited | Cheadle Hulme | 2023 |
| 3 NRG Ltd | London | 2025 |
| 3 Oak Wood Flooring TM Ltd | Hounslow | 2015 |
| 3 OCR Limited | London | 2018 |
| 3 Old School House Ltd | St Albans | 2021 |
| 3 Olden Lane Limited | Chislehurst | 2019 |
| 3 PDC Limited | Swansea | 2006 |
| 3 Peak Building Developments Ltd | Wolverhampton | 2026 |
| 3 Peaks Developments Ltd | Merthyr Tydfil | 2021 |
| 3 Phase Electrical Contractors Ltd | Stevenage | 2024 |
| 3 Phase Electrical Installations Ltd | Hythe | 2020 |
| 3 Phase Electrical Solutions Ltd | London | 2022 |
| 3 Phase Group Limited | Fareham | 2022 |
| 3 Phase Industrial Limited | Stratford-Upon-Avon | 2017 |
| 3 Pillar Land Limited | London | 2026 |
| 3 Pillars Civils Ltd | London | 2026 |
| 3 PIN Electrical Limited | Southampton | 2012 |
| 3 Planks Limited | Herne Bay | 2012 |
| 3 Point Building & Maintenance Ltd | Bristol | 2025 |
| 3 Point Construction Limited | Lincoln | 2013 |
| 3 Point Productions Limited | Sandy | 2016 |
| 3 Point Property Development Limited | Stowmarket | 2022 |
| 3 Property Group Limited | Manchester | 2024 |
| 3 R Construction & Property Development Limited | Loughborough | 1989 |
| 3 R'S Consulting Limited | Ashford | 2024 |
| 3 Rooms Installation Specialists Ltd | Leyland | 2018 |
| 3 Shires Builders Ltd | Sutton-In-Ashfield | 2022 |
| 3 Shires Construction Limited | Shropshire | 2005 |
| 3 Shires Group Limited | Beds | 2005 |
| 3 Sisters London Ltd | Leicester | 2017 |
| 3 Sixty Plant Hire Limited | London | 2017 |
| 3 Sixty Property Services Ltd | Solihull | 2006 |
| 3 Sixty Roofing and Property Maintenance Ltd | Guildford | 2023 |
| 3 Sixty Roofing Ltd | Doncaster | 2024 |
| 3 Sixty Training Ltd | Waterlooville | 2024 |
| 3 Solutions (2011) Limited | Wells | 2011 |
| 3 Spires Solutions Ltd | Burntwood | 2020 |
| 3 ST Andrew Square Apartments Limited | Edinburgh | 1988 |
| 3 Star Scaffolding Ltd | Hayes | 2016 |
| 3 Stars Homes Limited | Southampton | 2024 |
| 3 Step Designs Limited | Burgess Hill | 2015 |
| 3 Sugar House Lane Limited | London | 2019 |
| 3 Tee's Stars Maintenance Services Ltd | Gravesend | 2024 |
| 3 to 7 Star Street Ltd | Ware | 2014 |
| 3 Trees Houses Ltd | Hayes | 2020 |
| 3 Trojans Limited | Cardiff | 2022 |
| 3 U Projects Ltd | Batley | 2022 |
| 3 Upper Brook Street Management Company Limited | London | 1991 |
| 3 US Projects Ltd | Dewsbury | 2025 |
| 3 V Gold Ltd | Northampton | 2025 |
| 3 Way Building Services Limited | Rochdale | 2001 |
| 3 Way Handshake Ltd | Colchester | 2012 |
| 3 Way Maintenance Solutions Limited | Rochdale | 2005 |
| 3 Ways Railway & Construction Services Limited | South Ockendon | 2001 |
| 3 Willow Works Ltd | Halesowen | 2026 |
| 3 Wire Heating Ltd | Darlington | 2020 |
| 3 Wire Limited | Darlington | 2007 |
| 3 Wires Electrical Ltd | Northwood | 2026 |
| 3 Wires Electricians Ltd | Barnet | 2024 |
| 3-6-9 AK Ltd | Barnet | 2021 |
| 3-CS Projects Ltd | Harlow | 2022 |
| 3-D and ME Limited | Woodford Green | 2024 |
| 3-D Developments (Northern) Limited | Meltham | 1992 |
| 3-D Wyndows Limited | Blackdown | 1976 |
| 3-PHASE Electrics Ltd | Wellingborough | 2025 |
| 3-SPACE (UK) Limited | Weybridge | 2013 |
| 3.1STENGINEERING Ltd | London, England | 2025 |
| 3.2 Scaffolding Ltd | Old Cowyn | 2025 |
| 30 - 36 Vittoria Street Management Limited | Harrow | 2023 |
| 30 Cambridge Road Limited | Ely | 2014 |
| 30 Day Extensions Kingston Ltd | London | 2024 |
| 30 Day Extensions Limited | Wimbledon | 2018 |
| 30 Day Extensions Sales Ltd | Surbiton | 2024 |
| 30 Day Extensions Surbiton Ltd | Surbiton | 2024 |
| 30 Day Extensions Wandsworth Ltd | Wimbledon | 2019 |
| 30 Day Extensions Wimbledon Ltd | London | 2024 |
| 30 DEC 2020 PLC | Dartford | 2017 |
| 30 Pembridge Crescent Limited | London | 2025 |
| 30 RCG Limited | London | 2015 |
| 300 Builders Ltd | Mitcham | 2015 |
| 3000FT Water Energy Limited | Hampton | 2025 |
| 303 Automation and Electrical Engineering Ltd | Ossett | 2025 |
| 303 Electrical Limited | Cardiff | 2018 |
| 303 Flooring Limited | West Drayton | 2022 |
| 307 Builders Ltd | West Bromwich | 2024 |
| 308 Contracts Ltd | Clydebank | 2025 |
| 30IFM Ltd | Middlesbrough | 2025 |
| 30ONE-GROUP Ltd | Gloucester | 2018 |
| 31 Broad Street Properties Ltd | Penryn | 2019 |
| 31 Electrical Services Ltd | Nottingham | 2020 |
| 31 February Rail Limited | High Wycombe | 2016 |
| 31 Hawks Site Ltd | Walton-On-Thames | 2026 |
| 31 Landscapes Ltd | Oxford | 2019 |
| 31 Storeys Limited | Rickmansworth | 2018 |
| 31 Worcester Road Limited | Malvern | 2020 |
| 31-37 Disbrowe Road Freehold Company Limited | Newcastle Upon Tyne | 2012 |
| 310 Highbury Ltd | Waterlooville | 2021 |
| 310 ST James Road Limited | London | 2019 |