The terms and conditions of employment are for negotiation and agreement between employers and employees (or their representatives). Provided they do not discriminate unlawfully, for example on grounds of race, sex or disability, employers are free to offer the terms and conditions of employment which best suit their business needs.
Once agreed, they form a legally binding contract of employment. While it is always open to either party to seek to renegotiate the terms of the contract, if the employer changes any of the terms without the employee's agreement, the employee may be entitled to seek legal redress. We expect all employers, to treat employees fairly. Depending on the extent and likely impact of the proposed changes, employers should meet with affected employees or their trade union representatives, and explain their case for making the proposed change.
A guidance document which contains more information on the law in this area is available at www.gov.uk/browse/working. Employees may wish to seek independent legal advice, perhaps from their local Citizens Advice Bureau or law centre, if they are unclear on their contractual position.