Introduction
I felt that today's puzzle leaned a bit toward the difficult end of the scale - in part due to the rather convoluted wording of a few of clues.
Today's Glossary
Some possibly unfamiliar abbreviations, people, places, words and expressions used in today's puzzle
Colchester Native - the native oyster, ostrea edulis (when harvested in the Colchester fishery)
Foulness - an island on the east coast of Essex, England
Sir Peter Lely - 17th century Dutch painter
A review of today's puzzle by talbinho can be found at Times for the Times [ST 4354].
Commentary on Today's Puzzle
4a Not positive it's found, for example, in an oyster (8)
I puzzled for a long time over the wordplay here before feeling I really understood it. The definition is given by "not positive" (NEGATIVE). If we were to delete the word "found" from the clue, the wordplay would be quite straightforward, "It (the solution, NEGATIVE) is EG (for example) in NATIVE (an oyster)". However, when the word "found" is inserted in the clue, I find that I then need to mentally insert extra words in the clue for the cryptic reading to make sense to me, as follows, "It (the solution) is found by putting EG in NATIVE" or "It (the solution) is the result had one found EG in NATIVE".
Native is an informal reference to a native oyster, in the same way that one might refer to a McIntosh apple as a McIntosh or a Mac.
11a One promise nearly everyone makes (5)
At first, I thought this might be an example of the rarely seen & lit. clue. The clue itself is a definition of AVOWAL. The clue also contains the wordplay "A (one) VOW (promise) AL {ALL without the final L (nearly everyone)}". However, since the word "makes" seems to be superfluous to the cryptic reading, it appears that it does not completely satisfy the criteria for an & lit. clue.
16a Hole crab made, injuring him? (?)
Yet another clue that made me think. The solution is an anagram of HOLE CRAB, but is the anagram indicator made or made injuring? If the latter, then the definition would be the rather vague "him" signifying BACHELOR. However, if the former, why would "injuring him" mean BACHELOR?
At least I seem not to be alone in my thinking, as talbinho comments "
26a Disgusting state of Essex island? (8)
In his review, talbinho supposes that the solution to this clue is "
15d Mixed in tea, beer's held to set one against it (8)
When one sees an 's in a clue, one must decide whether it signifies a possessive (not in this case), a contraction for is (once again, not in this case), or a contraction for has (bingo). Since the latter is the case, ALE (beer) is the container in this container-type clue. Otherwise (i.e., if the 's had stood for is), ALE would have formed the contents.
Substituting
Signing off for this week - Falcon