Answer Base

My employer does not pay overtime they pay it on bank rate which is at a lesser rate-itis not a contract itis my normal job

This is legal only if you have the choice whether to do the bank work. your contractual work should be paid at your contracted rate - and that is the only work you are obliged to do (for example you could be contracted to work 35 hours per week) - any work offered to you at bank rate after the 35 hours can be refused by you.