Sarcasm can work, but it needs to be based on widely accepted truths that people can identify with.

Problems with great grandparent:

-Campaign finance is heavily regulated in the UK and about half of it comes from the state.

-UK media is less of a political frenzy. They have other things to talk about, like the premier league, or human affairs.

-The closest thing to US liberals language-wise are the Liberal Democrats, who are part of government. The closest thing to US liberals politically are the Conservatives (e.g., combating climate change is high on the conservative agenda)

-Liberals aren't gaining any seats in polls

That's a few too many errors for sarcasm to work.