Initially I thought this was the uncommon Jesselton registered mark R8. Then I remember a similar looking Beaufort postmark D6. On closer examination and especially with the larger lettering OV for nov in the top left corner, I have decided it is more likely to be the Beaufort cancellation. Both are very desirable postmarks. D6 was in use between 1923 and 1930. A pity it was not in coloured ink.
R8 has been under my nose all this time!. I examined my surplus stock book today and realized this smudged postmark which I had puzzled over many a time is in fact R8 with indistinct double outer rings. I wish I have a better example as R8 is rather rare and was in use between 1923-1926. I understand the value of this stamp may have been enhanced significantly.
Update I think it is a Beaufort D6.