To be a valid promissory note doesn't require a consideration. (A contract requires consideration, but a PN doesn't require a contract.)
I don't know about U.K. law, but in the U.S., lack of consideration is indeed a defense to a suit on a promissory note (with a huge caveat to be discussed below). UCC 3-303(b). But consideration doesn't have to be "equal," so arguably giving the maker of the note check books would be adequate consideration.
The maker of the note would also have a defense of fraudulent inducement (they were told the checks would work, and they don't. (But same caveat discussed below.)
However, I guess that someone purchasing a PN from Peter wouldn't succeed in a legal action against the maker to get the £150k.
A bona fide purchaser for value of a promissory note takes the note free of virtually all defenses that would have existed between the maker and the original payee, with only a few exceptions. UCC 3-305(b). But one defense that can be raised against a BFP is illegality of the underlying transaction. UCC 3-305(a)(1)(B).
Here, however, the dodgy language of the note (especially the part saying that sale of the note relieves the maker of liability) would probably preclude anyone from being a bona fide purchaser. See UCC 3-302(a). For the same reason, it would make the note unsaleable as a practical matter.
Dr. Caligari
(Du musst Caligari werden!)