Lying in politics, in certain contexts, is already punishable: lying to parliaments has consequences the world over. Lying to Congress, lying to a British parliamentary committee, ministerial ethics codes that punish misleading parliament, lying to the Australian parliament, it's all punishable in various ways.
The big question to answer is this: why should a politician be able to tell a demonstrable lie using their official communications, without consequence? Their official social media presence, their official political status twitter feed.
Why should politicians not be expected to colour only within the lines, like we used to expect them to do in the era before social media?
What, exactly, is the problem with punishing a flat out, demonstrable lie by a politician? Why do people not imagine that a bipartisan/multipartite commission or an ombudsman can't manage that, when we have effective ombudsmen in the UK that ensure basic truth (that is, not flat out lies or misleading claims) in advertising, truth in financial services claims, laws that prevent lying about curing cancer etc.?
Why does everyone -- particularly US HNers -- have to assume measures like this are intrinsically fascist? Just because your own politics is infected with the spiritual offspring of Lee Atwater and Charles Coughlin doesn't mean we have to accept that same downward spiral in our own.
People in the UK believe politicians should want to be held to a higher standard, and we'd like them to try to get back to how they behaved before foreign social media platforms enabled them to lie at scale like drunken sailors with impunity.