Since sale of goods is a gloss on the common law contract law, contract law has to be borne in mind.
If the description used is a mere representation then contract law applies - not s.13 - see
Harrison v Knowles & Foster (1918)
Cf Beale v Taylor (1967)
As always with mere representations and terms it is very difficult.
Relationship between s.13 and common law distinction between representations and contractual terms.