Recent work has suggested that when voters are less partisan, legislators engage in more personal vote-seeking. This has potentially important implications, given the widespread decline of partisanship in many countries, and the well-noted consequences of personal vote-seeking for policy-making, election results, and accountability. However, existing tests of this argument use either aggregate-level measures of partisanship, or constituency-level proxy measures. We thus lack direct evidence linking constituency-level partisanship to MPs’ parliamentary behaviour. To address this lacuna, this paper uses multilevel regression and poststratification (MRP) to produce new estimates of constituency-level partisanship in the UK. I then test the relationship between these estimates and British MPs’ legislative activity between 2010 and 2017. Contrary to previous studies, I find no evidence that MPs elected from less partisan constituencies engage in more personal vote-seeking. This null finding suggests that future work should explore whether existing proxies adequately measure partisan dealignment, as well as considering the conditions under which dealignment should and should not influence parliamentary behaviour.