I am employed on a written individual employment contract. This contract expired over a month ago, but I have continued working. My employer has offered me a new contract that reduces my pay. I have been told that unless I sign this contract, my employment will end because my contract has expired. Is this correct?

No. If you have worked on past the expiry date in your employment contract, your employment is now open-ended and can only be terminated if a justifiable reason exists and you are given reasonable notice of termination. You terms and conditions of employment will be the same as those in your written employment contract (except there will be no expiry date), and may only be changed if both you and your employer agree.