| Red Parrott Limited | Construction | 2015 |
| Red Squirrel Holdings Limited | Wholesale & retail | 2017 |
| Red Stag Homes Ltd | Construction | 2020 |
| Redbourn Capital Limited | Professional & scientific | 2017 |
| Redbourn Nails Limited | Other services | 2026 |
| Redders Asset Management Limited | Extraterritorial | 2011 |
| Redlance Management Limited | Real estate | 2002 |
| Redlap Designs Ltd | Professional & scientific | 2017 |
| Redplan Ltd | Extraterritorial | 2014 |
| Redpoint Energy Limited | Professional & scientific | 2013 |
| Redway HR Ltd | Professional & scientific | 2019 |
| Redwood Landscaping & Consultancy Services Limited | Other services | 2009 |
| Reed Mews (Redbourn) Management Company Limited | Households | 2026 |
| Reefview Limited | Professional & scientific | 1982 |
| Reflections Designlife Galery Ltd | Professional & scientific | 2020 |
| Regal PPF Limited | Wholesale & retail | 2024 |
| Regency Luxury Villas Limited | Households | 2013 |
| Regenevive Ltd | Agriculture & fishing | 2020 |
| Regenify Health Ltd | Health & social care | 2024 |
| Registered Offices (Herts) Limited | Administrative & support | 2019 |
| Reimaging Ltd | Professional & scientific | 2026 |
| Reiwa Studios Limited | Wholesale & retail | 2025 |
| Rejuvenation Redefined Limited | Other services | 2009 |
| Release Efficiency Limited | Administrative & support | 2020 |
| Remarkable Holdings Limited | Professional & scientific | 2006 |
| Remephy Technologies Ltd | Agriculture & fishing | 2024 |
| Remote-Solutions.Tv Limited | Professional & scientific | 2011 |
| Rempapa Limited | Manufacturing | 2018 |
| Renatowo Ltd | Real estate | 2026 |
| Renee Charlton Acupuncture Limited | Health & social care | 2023 |
| Rent a Tree Limited | Agriculture & fishing | 2023 |
| RES Construction Services Ltd | Construction | 2022 |
| Resilient Technology Specialists Ltd | Wholesale & retail | 2020 |
| Resilimy Limited | Professional & scientific | 2022 |
| Resin London Driveways Ltd | Construction | 2025 |
| Resinbound Group Ltd | Construction | 2024 |
| Retail Bright Consultancy Limited | Professional & scientific | 2024 |
| Retro Vintage Limited | Professional & scientific | 2012 |
| Revega Ltd | Wholesale & retail | 2011 |
| Revival Decorative Paint Effects Ltd. | Real estate | 1994 |
| Reynoldsco Limited | Health & social care | 2019 |
| RF Techworks Ltd | Professional & scientific | 2026 |
| Rhia London Limited | Manufacturing | 2024 |
| Rhymegold Limited | Households | 2008 |
| Riaz MP Services Limited | Real estate | 2026 |
| Richard Boast Associates Limited | Professional & scientific | 1996 |
| Richard Brown Ltd | Professional & scientific | 2007 |
| Richards Cakes (Holdings) Limited | Financial services | 1988 |
| Riders in Gear Ltd | Wholesale & retail | 2020 |
| Ridge Scaffolding Company Limited | Construction | 2022 |
| Ridgewood Contractors Limited | Construction | 2010 |
| Ridgmont House Maintenance Company Limited | Households | 1985 |
| RIFT2MES Ltd | Professional & scientific | 2018 |
| Ripcord Designs Limited | Professional & scientific | 2015 |
| Ripple Precision Ltd | Information & communication | 2018 |
| Riresto Real Estate Ltd | Real estate | 2025 |
| Riseley Plumbing Services Limited | Construction | 2003 |
| Rising Lifters Limited | Information & communication | 2023 |
| Riskinsur Limited | Information & communication | 2018 |
| Riskmetrica Limited | Information & communication | 2025 |
| Riverton Capital Limited | Information & communication | 2015 |
| Riverton Partners Limited | Information & communication | 2015 |
| Rizzello Creative Limited | Professional & scientific | 2020 |
| RJB Finance Consulting Limited | Professional & scientific | 2014 |
| RJR Slater Limited | Health & social care | 2023 |
| Rlcm Property Consultants Limited | Professional & scientific | 2020 |
| Rmir Investment Limited | Real estate | 2026 |
| Road-Pro Limited | Wholesale & retail | 1981 |
| Roadscan Limited | Wholesale & retail | 2006 |
| ROB Casey Lighting Design Limited | Administrative & support | 2014 |
| ROB Clarke Design Limited | Professional & scientific | 2008 |
| ROB Ivey Limited | Manufacturing | 2016 |
| Robbo Consulting Limited | Information & communication | 2024 |
| Robert Moreland Ltd | Financial services | 2003 |
| Roberts Family Property Holdings Limited | Real estate | 2021 |
| Robin Court Freehold Limited | Real estate | 2001 |
| Robinson Rigging Limited | Administrative & support | 2023 |
| ROCA5 Ltd | Real estate | 2022 |
| Rockbridge Infrastructure Limited | Professional & scientific | 2026 |
| Rocket 45 Limited | Construction | 2021 |
| Rocking Consulting Limited | Information & communication | 2018 |
| Rococo Landscaping & Building Ltd | Construction | 2006 |
| ROI Investments Ltd | Households | 2022 |
| Rojiroti UK | Health & social care | 2011 |
| Roman City Ltd | Hospitality | 2015 |
| Room Design + Studio Ltd | Professional & scientific | 2019 |
| Root and Rise Studio Ltd | Extraterritorial | 2024 |
| ROP International Company Ltd | Other services | 2021 |
| Rory Browne Artist Ltd | Arts & recreation | 2023 |
| Rose and Crown Welwyn Limited | Hospitality | 2019 |
| Rosehill Place Management Company Limited | Real estate | 2025 |
| Roseness (Freehold) Limited | Households | 2022 |
| Roseveare Flat Management Company Limited | Households | 1981 |
| Rosie Oulton and Co Limited | Professional & scientific | 2023 |
| Rosspalm Limited | Information & communication | 2022 |
| Rothamsted Court (Harpenden) Limited | Real estate | 1985 |
| Rothamsted Enterprises Limited | Administrative & support | 1999 |
| Rothamsted Experimental Station Limited | Administrative & support | 2002 |
| Rothamsted International Consulting Limited | Professional & scientific | 1998 |
| Rothamsted Research Holdings Limited | Administrative & support | 1997 |