I think you'll find, the way things are going, the only way this leaflet was "misleading and biased" is in how it toned-down the consequences of Brexit.
The remain campaign have not been convicted of breaking the law. Not for breaking electoral law, nor for breaking direct market rules. Anyone can dispute this by contacting the Electoral Commission and the ICO. Nobody has because the remain camp weren't devoid of ethics and veracity during the referendum campaign.