This chapter examines the impact of the unprecedented COVID-19 restrictions on loneliness. Analysing large-scale UK panel data, we demonstrate a longitudinal association between policy stringency and loneliness, partially explained by changes in home confinement, in-person contact, and perceived social support. Examining loneliness trajectories between March and August 2020, we find that loneliness increased gradually throughout the first national lockdown, peaking at its end before decreasing as restrictions eased. This indicates that loneliness accumulated under prolonged physical isolation rather than being an acute initial response. Lockdown termination provided only modest immediate relief, particularly for those living alone, who were disproportionately affected. Our findings contribute to understanding changes of loneliness and highlight the need of targeted support for those living alone in future pandemics requiring isolation measures.