Behavioural economics (a combination of economics and psychology) provides keys to understand decisions made by politicians and citizens along the COVID-19 pandemic through the so-called cognitive biases. These biases can be offset by implementing behavioural interventions named "nudges" in order to promote responsible behaviours in the "new normality". This paper analyses, from a behavioural economics perspective, past, present and future of behavioural aspects surrounding the pandemic. Besides, this paper proposes different ways to formalize nudges according to law, which needs the fulfilment of three minimum requirements, namely: transparency, non-arbitrariness and efficiency. Furthermore, it is also suggested that protocols and contingency plans are set up to face future pandemics, in which both soft (nudge-type) interventions and hard legal regulations play different roles but complementary ones. Nudges can be implemented in a fast and less coercive way, so they are particularly suitable for changing mild misbehaviour, reserving legal sanctions for the more serious ones.