| Code | Name | Region |
|---|---|---|
| GBOLW | Old Woking | SRY |
| GBOWT | Old Wolverton | MIK |
| GBOBY | Oldbury | WAR |
| GBODH | Oldham | OLD |
| GBOMU | Oldmeldrum | ABD |
| GBOLR | Ollerton | NTT |
| GBNTN | Nuneaton | WAR |
| GBNUN | Nunthorpe | MDB |
| GBNUR | Nursling | HAM |
| GBNBN | Nutbourne | WSX |
| GBXNU | Nutfield | SRY |
| GBNH9 | Nuthampstead | HRT |
| GBVTJ | Nuthempstead | |
| GBXOA | Oadby | LEC |
| GBXOK | Oakamoor | STS |
| GBOKM | Oakham | LEC |
| GBOAK | Oakhamness | |
| GBOKG | Oakhanger | HAM |
| GBOKL | Oakley | HAM |
| GBOKW | Oakworth | BRD |
| GBOAR | Oare | WIL |
| GBOBA | Oban | AGB |
| GBOHA | Ockham | SRY |
| GBOCL | Ockley | SRY |
| GBODT | Oddington | OXF |
| GBODD | Oddsta, Fetlar | ZET |
| GBNHI | Northiam | ESX |
| GBNLH | Northleach | GLS |
| GBNOW | Northlew | DEV |
| GBNME | Northmavine | ZET |
| GBNHT | Northolt | EAL |
| GBNTH | Northwich | CHW |
| GBNWD | Northwood | HIL |
| GBNOO | Norton | HEF |
| GBZCM | Norton | KEN |
| GBNOT | Norton | NYK |
| GB7TR | Norton | WOR |
| GBNCN | Norton Canes | STS |
| GBDSY | Norton Disney | |
| GBNFZ | Norton Fitzwarren | SOM |
| GBNOL | Norwell | NTT |
| GBNRW | Norwich | NFK |
| GBZCN | Norwood | CRY |
| GBXNG | Nottage | BGE |
| GBNHL | Notting Hill | KEC |
| GBNTG | Nottingham | NTT |
| GBNMK | North Muskham | NTT |
| GBNOQ | North Queensferry | FIF |
| GBNRR | North Roe To Hillswick | ZET |
| GBNRO | North Ronaldsay | ORK |