The four pattern leaflets were, as you would expect, advertised in Vogue Knitting. Oddly, one of the other patterns is modelled in the ad by Twiggy, I think - hard to be sure, because her face is partly hidden by a large flower. The model on the leaflet is definitely not the same person. Wonder why they switched models?
It's unusual to see the top fashion models, who normally inhabit the glossy magazines, appearing on pattern leaflets. But in 1969, Marisa Berenson also appeared on a Hayfield leaflet. Like Grace Coddington, she was seen frequently in Vogue at that time, and appeared on several Vogue covers, for instance in July 1970. In the 1970s, she moved into acting and appeared in several films.
The Marisa Berenson leaflet was featured in a Hayfield ad, and perhaps that was the reason for choosing a top model. It seems to have been a special case - as far as I know, she did not model for any other Hayfield leaflets, or for any other spinners' leaflets. She can rarely have modelled anything as mundane as an Aran cardigan.