Interpersonal influences on cognition can distort memory judgements. Two experiments examined the nature of these ‘social’ influences, and whether their persistence is independent of their accuracy. Experiment 1 found that a confederate’s social proximity, as well as the content and the confidence of their utterances, interactively modulate participants’ immediate conformity. Notably, errant confederate statements that ‘lied’ about encoded material had a particularly strong immediate distorting influence on memory judgements. Experiment 2 revealed that these ‘lies’ were also memorable, continuing a day later to impair memory accuracy, while accurate confederate statements failed to produce a corresponding and lasting beneficial effect on memory. These findings suggest that an individual’s ‘informational’ social influence can be selectively heightened when they express misinformation to someone who suspects no deceptive intent. The methods newly introduced here thus allow multiple social and cognitive factors impinging on memory accuracy to be manipulated and examined during realistic, precisely controlled dyadic social interactions.