Interesting analysis from NHS of a series of surveys.
Sustain has produced publications which have focused on the marketing practices of junk food manufacturers to school children.
Another factor is increasing size of packets. This Cochrane review from the University of Cambridge found using data from 72 studies and over 6,700 participants, showed that people consume more food and non-alcoholic drink when offered bigger portions, bigger packaging, or bigger tableware rather than smaller sizes.
The location of crisps in the shops also effects consumption. This 2018 study from the University of Cambridge found that if packets were located near the checkout people bought and ate more chocolate and crisps.