Your contract of employment will contain an express term specifying your rate of pay, which is a matter of agreement between you and your employer. In accepting the contract of work, you also accept the offered pay rate.
As long as they offer at least the national minimum wage requirements, and do not conflict with Equal Pay legislation between men and women doing the same job, they are free to offer different pay scales and patterns, based on other factors such as:
In the case of agency workers, pay rates are a matter for your employer and the agency concerned to determine. A higher hourly and daily rate for agency staff may also reflect in part the fact that these workers are only paid for when they work and do not have access to the other occupational benefits that a firm's core workforce may benefit from (such as occupational pensions, sick pay and maternity entitlements, etc).
One other restriction on pay differentials may result from a collective pay agreement between the employer and a union, in which case you should consult your workplace union.
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