| Code | Name | Region |
|---|---|---|
| GBMES | Medstead | HAM |
| GBMFY | Meikle Ferry | HLD |
| GBMEL | Melbourn | CAM |
| GBMBE | Melbourne | DBY |
| GBMLU | Melbourne | ERY |
| GBMLD | Meldreth | CAM |
| GBMAO | Marston | LIN |
| GBMRN | Marston | OXF |
| GBMTS | Marston | WIL |
| GBMRG | Marston Green | SOL |
| GBMMG | Marston Magna | SOM |
| GBMMC | Marston Moretaine | CBF |
| GBMTT | Marston Trussell | NTH |
| GBMRM | Martham | NFK |
| GBMHM | Martlesham | SFK |
| GBMHT | Martlesham Heath | SFK |
| GBMLE | Martley | WOR |
| GBZOR | Martock | SOM |
| GBMRB | Maryfield, Bressay | ZET |
| GBMBO | Marylebone | WSM |
| GBMRY | Maryport | CMA |
| GBMTN | Maryton | ANS |
| GBMAS | Masham | NYK |
| GBMTG | Matching Green | ESS |
| GBMAF | Matfield | KEN |
| GBMTL | Matlock | DBY |
| GBMKL | Market Hill | ARM |
| GBMAT | Market Lavington | WIL |
| GBMOV | Market Overton | RUT |
| GBMKR | Market Rasen | LIN |
| GBMWE | Market Weighton | ERY |
| GBMRH | Markethill | ARM |
| GBMFL | Markfield | LAN |
| GBMRK | Markinch | FIF |
| GBMKS | Marks Tey | ESS |
| GBMRL | Marlborough | WIL |
| GBMSO | Marlesford | SFK |
| GBMLW | Marlow | BKM |
| GBMA9 | Marnhull | DOR |
| GBMZL | Marple | SKP |
| GBMAK | Marrick | NYK |
| GBMSN | Marsden | KIR |
| GBMGB | Marsh Gibbon | BKM |
| GBMSJ | Marshland Saint James | NFK |
| GBMKY | Marske-by-the-sea | RCC |
| GBMN8 | Marston | CHW |
| GBMEA | Manea | CAM |
| GBXMN | Mangotsfield | LIN |
| GBMNN | Manningtree | ESS |
| GBMFD | Mansfield | NTT |