Percival,
If you had a fixed term contract, which I am guessing as you say that you didnt sign the new contract, under English Law, the terms and conditions of that contract would have "died" at the end of the contract.
It is then up to you, if offered a new contract, as opposed to an extension, to agree new terms and conditions.
If your salary and per diems have been halved it may be that those are the new contract terms which you are at liberty to reject or accept.