If i haven't signed a contract at my work and the company demote me, can they cut my wages?

I've been in my postion for 2 years and been with the company for nearly 5 years. I've not had any written warnings and have been told verbally my standard in performance has dropped. Without any further noticed i was told i was being demoted. The reason was i couldn't do the job to the same standard anymore. Can u tell me where i stand with this because very complicated from my view and i don't want to have to take this step backwards.