Short term contract - is this clause acceptable?

[The Lone Gunman]

Doing something like that will land you squarely in IR35 territory. An obligation for the client to pay you even when there is no work makes you look a lot like a permie.

*Hint* If the contract is for 6 months, and the client thinks it will take six months then it is your duty as a contractor to meet their expectations *hint*

Not if he quotes a price for the job in the first place. Fixed price work = opportunity for profit/loss = proper business = no IR35.