Background: In May 2016, along with the latest European Tobacco Products Directive (TPD), standardised packaging legislation was implemented in the UK. During the following 12-month transition period, both new and old types of packaging were allowed on the market. This study aimed to assess awareness of standardised packaging and other TPD changes in the UK population in March 2017, when both forms of packaging were in widespread use. Methods: We conducted two surveys—one in adults and one in young people—investigating awareness of plain packaging legislation. In young people, we also measured susceptibility to smoking using previously validated questions. We asked smokers whether they had recently changed the product they used and also whether they used any of the products that are banned by the new legislation. Results: In the adult survey, 73.5% (95% CI: 71.5–75.5%) of the participants were aware of the new legislation and 32.4% (95% CI: 30.3–34.5%) had noticed changes in tobacco packaging, this proportion being considerably higher among smokers (83.7%; 95% CI: 78.9–87.5%) than never smokers (20.7%; 95% CI: 18.2–23.4%). More than half (52.4%; 95% CI: 46.5–58.4%) were using pack sizes or shapes (typically less than 20 cigarettes or 30 g loose tobacco), that would become illegal after full TPD implementation, and 31.4% (95% CI: 26.2–37.1%) reported switching to a different product since October 2016, in most cases to a cheaper brand. Among young people, 20.2% (95% CI: 17.8–22.7%) reported that they had noticed standardised packaging, comprising 16.2% (95% CI: 13.7–19.0%) of non-susceptible never smokers, 25.6% (95% CI: 18.0–35%) of susceptible never smokers, and 49% (95% CI: 37.8–60.2%) of ever smokers. Conclusions: In the final stages of implementation, awareness of the introduction of standardised packs was highest among smokers. The TPD will cause nearly half of adult smokers to purchase larger packs, and may cause many smokers to switch to cheaper brands