| Infrabee Infrastructure Partners Ltd | Hereford | 2023 |
| Infrapa Ltd | St. Albans | 2011 |
| Infrared Replacing GAS Ltd | Thirsk | 2020 |
| Infrastrata Energy UK Limited | London | 2019 |
| Infrastructure Corridor Energy Ltd | Tamworth | 2023 |
| Infused Solar Energy Ltd | London | 2026 |
| Ingendehsa Investments Ltd | Norwich | 2025 |
| Ingine Wave Energy Systems Ltd | Thurso | 2016 |
| Ingmanthorpe Energy Limited | Manchester | 2013 |
| Inish Glow Limited | Belfast | 2015 |
| Inishative Windfarm Limited | Belfast | 2010 |
| Inkersall Solar Farm Limited | London | 2019 |
| Innasol SPV1 Limited | Chelmsford | 2025 |
| Innasol Super Power One Ltd | Chelmsford | 2017 |
| Inner Dowsing Wind Farm Limited | Aberdeen | 2000 |
| Innerhadden Hydro Limited | Pitlochry | 2005 |
| Innolivio Ltd | Okehampton | 2013 |
| Innova Energy II Limited | Cheltenham | 2022 |
| Innova NG Operations Ltd | Cheltenham | 2023 |
| Innova Renewables Limited | Cheltenham | 2019 |
| Innovat Energy Limited | London | 2025 |
| Innovation Power Hire Limited | Durham City | 1997 |
| Innovation Power Limited | Durham City | 2013 |
| Innovative Electrical & Solar Solutions Ltd | Hartlepool | 2025 |
| Innovative Roofing & Solar Ltd | Hartlepool | 2025 |
| Innovergy UK Limited | Leamington Spa | 2023 |
| Innowatt Ltd | London | 2020 |
| Inovyn Energy Limited | Runcorn | 1986 |
| Inpex Europe Limited | London | 2021 |
| Inpex Renewables UK Holdings ME Limited | London | 2018 |
| Inrange AZ Fulfilment Energy SPV Ltd | London | 2026 |
| Inrange Data Centre Energy SPV Ltd | London | 2026 |
| Inrange Distributed Energy Holdco Limited | London | 2026 |
| Inrange Energy Assets Holdco Ltd | London | 2025 |
| Inrange Energy Assets SPV 1 Ltd | London | 2025 |
| Inrg (Solar Parks) 15 Ltd | London | 2013 |
| Inrg Solar Parks Ltd | London | 2014 |
| Inserco Industrial (Controls) Limited | Rainham | 2003 |
| Inshinagh Lane Ltd | Ballymoney | 2012 |
| Inside Air Limited | Cannock | 2006 |
| Insight Air Conditioning Limited | Maidstone | 2021 |
| Inspirational Consulting Ltd | Worthing | 2010 |
| Inspire Energy Associates CME Ltd | Alfreton | 2025 |
| Inspire Utilities Ltd | Preston | 2021 |
| Insta Energy 67 Ltd | Oldham | 2025 |
| Instacool Limited | Braintree | 2015 |
| Installation Contract Engineers Limited | Southampton | 1998 |
| Instant Grid Ltd | York | 2026 |
| Instavolt Limited | Basingstoke | 2016 |
| Instelek Ltd | Todmorden | 2017 |
| Intake Electrical Contractors Limited | Rotherham | 2008 |
| Intake Energy Limited | Skipton | 2012 |
| Integra Alternative Investments Ltd | London | 2023 |
| Integra QME 1 Limited | Scarborough | 2017 |
| Integrated Acquisitions & Business Bureau Ltd | Bromley | 2025 |
| Integrated Energy Holdings Limited | London | 2016 |
| Integrated Energy Infrastructure Limited | Cardiff | 2025 |
| Integrum SPV 21004 Limited | Rugby | 2022 |
| Integrum SPV 21014 Limited | Rugby | 2022 |
| Integrum SPV 22029 Limited | Rugby | 2022 |
| Integrum SPV 22051 Limited | Rugby | 2024 |
| Integrum SPV 22153 Limited | Rugby | 2023 |
| Integrum SPV 22298 Limited | Rugby | 2022 |
| Integrum SPV 22451 Limited | Rugby | 2023 |
| Integrum SPV 22455 Limited | Rugby | 2022 |
| Integrum SPV 22566 Limited | Rugby | 2023 |
| Integrum SPV 22571 Limited | Rugby | 2023 |
| Integrum SPV 22790 Limited | Rugby | 2024 |
| Integrum SPV 23101 Limited | Rugby | 2024 |
| Integrum SPV 24002 Limited | Rugby | 2024 |
| Intelec Solar and Electrical Ltd | Abergavenny | 2025 |
| Intelegen Limited | Glastonbury | 2022 |
| Intellergy Ltd | Raglan | 2021 |
| Intelligent Air Conditioning Ltd | Woking | 2010 |
| Intelligent GAS and Power Ltd | Cramlington | 2018 |
| Intelligent Green Energy Limited | Belfast | 2016 |
| Intelligent Green Energy Two Limited | Belfast | 2016 |
| Intelligent Installations Limited | St. Ives | 2016 |
| Intelligent Tomorrow Ltd | Redhill | 2022 |
| Intelligent Valves Ltd | Haywards Heath | 2021 |
| Intellivolt Limited | London | 2026 |
| Inter-Electrical Services Limited | Pontrhydyrun, Cwmbran | 2000 |
| Intercity GAS Limited | Hayes | 2010 |
| Intergen Enterprises (UK) Ltd. | London | 1998 |
| Interiors (E&W) Ltd. | Edinburgh | 2021 |
| Interkool Refrigeration & Air Conditioning Ltd | North Shields | 2015 |
| Intermech Limited | Bristol | 2015 |
| Internal Environments Southern Limited | Fareham | 2013 |
| Internal Facilities Limited | Fareham | 2017 |
| Internal Solutions (Southern) Limited | Fareham | 2019 |
| International A&A Ltd | Teddington | 2025 |
| International Brazilian Petroleum UK Ltd | Brentford | 2021 |
| International Clean Energy Ltd | London | 2023 |
| International Energy Co Ltd | London | 2022 |
| International Innovations Development Projects Ltd | London | 2019 |
| International Power Global Developments Limited | London | 1992 |
| International Power Group Limited | York | 2025 |
| International Power Retail Supply Company (UK) Limited | 1 Oxford Street | 2007 |
| Interparex Investment Ltd | London | 2010 |
| Intrinsic Energy Group Ltd | London | 2026 |