| Oldboy Ltd | Bradford | — | — | Open → |
| Oldham Metropolitan Borough Council | Oldham | building.control@oldham.gov.uk | x | Open → |
| OLDRIDGE | — | — | — | Open → |
| Oldridge & Longfield Roofing | Goole | — | — | Open → |
| Oliver Johnson | Leeds | — | — | Open → |
| Oliver Bayliss | Harrogate | Oliver_bayliss@outlook.com | — | Open → |
| Oliver Schaller | York | — | — | Open → |
| OLIVER STOWE | — | — | — | Open → |
| OLLIE SCOGNAMIGLIO | — | — | — | Open → |
| OLUOYEDE | — | — | — | Open → |
| Orinder Chohan | Leeds | — | — | Open → |
| Owl Architecture | Leeds | — | — | Open → |
| Owl Property Development Ltd | Lincolnshire | owlpropertydevelopment@gmail.com | — | Open → |
| Oxford City Council | Oxford | buildingcontrol@oxford.gov.uk | 01865 252807 | Open → |
| Oxfordshire Fire & Rescue Service | Kidlington | — | — | Open → |
| P & N Designs | Brough | — | — | Open → |
| P BROCKWELL | — | — | — | Open → |
| P Gardham Ltd Building Contractors | York | alan@pgardhamltd.co.uk / steve@pgardhamltd.co.uk | Steve Gardham mob. 07584 128390 | Open → |
| P GIBBONS & M SCOTT | — | — | — | Open → |
| P H Carr & Sons | York | — | — | Open → |
| P H Carr & Sons | York | — | — | Open → |
| P Huxford & M Brown | York | — | 07979611763 | Open → |
| P JACKSON | — | — | — | Open → |
| P LANCASTER | — | — | — | Open → |
| P N Bakes Architectural Consultancy | Bradford | philbakes@aol.com | — | Open → |