How do legislators respond to constituents' requests? Recent studies showcase that US legislators are particularly responsive to their voters, even tailoring their messages toward them. But little research investigates if these findings hold for parliamentary systems which are characterized by high party discipline forcing legislators to fall in line. We theorize that in such systems legislators use their party as a shield if their opinion contradicts their constituents' positional wishes. We test our argument in an audit study involving both legislators and actual voters during the Brexit negotiations in 2019 in the United Kingdom. Contrary to conventional wisdom about party-dominated systems we find no evidence that MPs are less responsive to correspondence from party-incongruent constituents nor that they use their party as a shield. These null findings have important implications for our understanding of how legislative behavior in parliamentary systems is (not) constrained by party discipline.