[EDIT 2/4: changed subject line]
I recently acquired this registered letter and would like help in getting an identification and catalog value for the 2p stamped envelope.

The cover is addressed to Professor A(rthur) S(ampson) Napier of Headington Hill, Oxford (biographic information on Napier, then a professor of English at Oxford University is at the following link
http://www.headington.org.uk/histor...cotuit.htm). Tied to the cover by a double strike of a 28 June 1892 Alderly Edge duplex postmark is an 1881 1p lilac (16 dots) (Scott 89). There is also a registered transit mark on the face in which what should be the "C" in "Manchester" appears to be a "D".

The reverse contains an Oxford receiving stamp, and the flap has the embossed 2p registration stamp, which I'd like help with in terms of both identification and value.

Any help would be greatly appreciated!
Steve