Gents,
The following link should take you to the RCEME Association website, Handbooks page:
https://drive.google.com/drive/mobil...13&direction=a
Beginning on page 22 of “CAMT 11-1 1962.pdf” you can find a number of org charts and descriptions of the various RCEME units that existed at the time.
If this is the correct time period then I will suggest that “27” translates to “Workshop Branch, 27 Central Ordnance Depot, London”.
I believe there have been other questions on this forum regarding workshop numbers. Perhaps someone with better computer skills can obtain and post images of the Org charts for future reference?