I looked into it and looks to be a hoax but do your own research. Funny ad all the same as the real joke is that is not an unreasonable goal and why have we not yet? Would be nice as the current homeless response is a lose lose for all parties.
For the party (and currently government of the UK) "sponsoring" the fake ad, directly murdering homeless people by chopping them in half would be pretty on-brand, they pretty much kill them off indirectly with legislation already and disparage the homeless in the media all the time.
I agree that halving homelessness would be of benefit to everyone, but the Tories don't particularly care about benefit to anyone apart from themselves and their masters.
That would be "cut homelessness in half" or "cut the number of homeless people in half". That's very different from "cut all homeless people in half", which would be bisecting each homeless person. This is clearly a joke about conservatives being heartless monsters, right?
Or is this a dialectal grammar difference between UK and US English?