I work in NHS,but am paid much less than my colleagues for the same work and time?

The problem is you probably signed a contract indicating how much money you will be paid, correct? Even if everyone else is doing the exact same work and time as you, maybe they bargained for a higher pay than you. Basically, there is nothing that you can do about your pay, even if they VERBALLY said it would be corrected. Unless you have something in writing indicating that they will correct it. Lastly, why did YOU allow them to wait a year?