| PO Number | Town / Place name | Code |
|---|---|---|
| 500 | Haslingden | |
| Keymer | ||
| 501 | Rawstenstall | |
| 502 | Stalybridge | |
| 503 | Manningtree | |
| 504 | Mansfield | |
| 505 | March | |
| 506 | Margate | |
| 507 | Marazion | |
| 508 | Market Deeping | |
| 509 | Market Drayton | |
| 510 | Woore | |
| 511 | Market Harborough | |
| 512 | Market Raisen | |
| Market Rasen | ||
| 513 | Market Street | |
| Merstham | ||
| 514 | Market Weighton | |
| 515 | South Cave | |
| Warlingham | ||
| Whyteleafe | ||
| 516 | Marlborough | |
| 517 | Great Bedwin | |
| 518 | Marlow | |
| 519 | Maryport | |
| 520 | Matlock Bath | |
| 521 | Melksham | |
| 522 | Melton Mowbray | |
| 523 | Merthyr Tydfil | |
| 524 | Middlewich | |
| 525 | Holmes Chapel | |
| 526 | Winsford | |
| Boston Spa | ||
| 527 | Midhurst | |
| 528 | Mildenhall | |
| 529 | Milford | |
| Milford Haven | ||
| 530 | Milnthorpe | |
| 531 | Mold | |
| 532 | Monmouth | |
| 533 | Ragland | |
| Raglan | ||
| 534 | Moreton-in-Marsh | |
| 535 | Stow on the Wold | |
| 536 | Winchcombe | |
| 537 | Morpeth | |
| 538 | Namptwich | |
| Nantwich | ||
| 539 | Narberth | |
| 540 | Neath | |
| 541 | Newark | |
| 542 | Southwell | |
| 543 | Carlton-on-Trent | |
| Liss | ||
| 544 | Newbury | |
| 545 | Newcastle on Tyne | |
| Quayside Newcastle on Tyne | ||
| 546 | Newcastle-under-Lyne | |
| Newcastle, Staffs | ||
| 547 | Stoke | |
| Stoke on Trent | ||
| 548 | Tunstall | |
| 549 | Hanley | |
| 550 | Cobridge | |
| Kenley | ||
| 551 | Burslem | |
| 552 | Lane Delph | |
| Sandgate | ||
| 553 | Lane End | |
| Longton | ||
| 554 | Etruria | |
| 555 | Long-Port | |
| 556 | Shelton | |
| 557 | Newmarket | |
| 558 | Newnham | |
| 559 | Lydney | |
| 560 | Newport, IOW | |
| 561 | Newport, Mon (C) | |
| Newport Docks Newport, Mon | ||
| 562 | Caerleon | |
| 563 | Tredegar | |
| 564 | Newport Pagnell | |
| 565 | Newport, Salop | |
| 566 | New Romney | |
| 567 | Newton Abbot | |
| 568 | Newtown | |
| 569 | Northallerton | |
| 570 | Northampton | |
| 571 | Northleach | |
| 572 | Andoversford | |
| 573 | Andoversford | |
| Wighton | ||
| 574 | North Shields | |
| 575 | Norwich | |
| 576 | Acle | |
| Rolvenden | ||
| 577 | Cromer | |
| 578 | Loddon | |
| Appledore, Kent | ||
| 579 | North Walsham | |
| 580 | Reepham | |
| Lamberhurst | ||
| 581 | Scatton | |
| Burnham, Som | ||
| 582 | Worstead | |
| Naguabo, Porto Rico | ||
| 583 | Nottingham | |
| 584 | Bingham | |
| Woodchurch | ||
| 585 | Ilkeston | |
| 586 | Stapleford | |
| Bowness, Westm'land | ||
| 587 | Oakham | |
| 588 | Oakhampton | |
| Okehampton | ||
| 589 | Hatherleigh | |
| Grasmere | ||
| 590 | Odiham | |
| Billingshurst | ||
| 591 | Oldham | |
| 592 | Ollerton | |
| 593 | Ormskirk | |
| 594 | Southport | |
| 595 | Oswestry | |
| 596 | Cerrig-y-druidon | |
| Fittleworth | ||
| 597 | Llanwrst | |
| 598 | Pentre Voylas | |
| 599 | Otley |