By the mid-1930s, the BMMO network was expanding rapidly and the company were starting to run out of available service numbers. To free up numbers for new services, local area networks were renumbered with a prefix letter to represent the area when the network operated, so thus on Monday 7th January 1935 all local Malvern area services were renumbered in the range M10–M30 (with service number M13 being omitted for some reason. Unlucky?).
With the renumbering of local Malvern area services on Monday 7th January 1935, Service 377 running between Great Malvern, Wyche Cutting, and Colwall Green became Service M27. The service had first been introduced on Wednesday 30th May 1928 as a short-working variation of Service 477, which ran between Hereford, Ledbury, Colwall Green and Great Malvern.
At the same time, Service 367 was renumbered to Service M17. This was a short-working variation running only between Great Malvern and Wyche Cutting.
All Service M27 journeys were renumbered to Service 477 on Monday 26th April 1976.
1 Journeys terminating at Wyche Cutting operated as Service M17.
| M | 2 | 7 |
| New January | 1935 | Great Malvern ↔ Wyche Cutting ↔ Colwall Green | |
| June | 1957 | Great Malvern ↔ Wyche Cutting ↔ Colwall Green | |
| March | 1972 | Great Malvern ↔ Wyche Cutting ↔ Colwall Green | |
| January | 1974 | Great Malvern ↔ Wyche Cutting ↔ Colwall Green |