Take a look at your contract.if it states 25 hours then thats your contracted hours.No one can enforce more or less hours without your agreement (new contract of hours )
They also can not change your workplace without your agreement.
An employer cannot force you to work more hours if your contract specifies fixed working hours, unless you agree to the change or a valid contractual clause allows it.
​Your Rights in This Situation
​1. Fixed Contracted Hours Require Your Consent
If your contract states a specific number of weekly hours (e.g., 30 hours a week), increasing those hours is a change to your terms of employment (a variation of contract). Your employer must consult with you and obtain your agreement. You have the right to say no.
​2. Check for Overtime or "Flexibility" Clauses
​Compulsory Overtime: Check if your contract mentions mandatory overtime or additional hours "as required by the business." Even if it does, the total hours must still comply with legal limits and remain reasonable. ​Flexibility Clauses: General phrases allowing the employer to change terms rarely give them unlimited power to permanently add significant hours to your schedule.
​3. Maximum Weekly Working Time (48-Hour Limit)
Under UK law (Working Time Regulations), you cannot be forced to work more than an average of 48 hours per week unless you have voluntarily signed a written opt-out agreement. If you haven't signed an opt-out (or choose to cancel it), they cannot legally compel you to exceed this limit.
​4. Protection Against Indirect Discrimination
If working extra hours is difficult due to protected characteristics—such as caring responsibilities (childcare/eldercare), a disability, or religious commitments—forcing the increase on you could constitute indirect discrimination. Employers must consider reasonable requests or adaptations.
​Recommended Steps to Refuse the Extra Hours ​Review Your Contract: Double-check your core contracted hours, overtime clauses, and notice terms. ​Have an Informal Conversation First: Tell your manager clearly that you cannot take on the extra hours. Focus on clear, objective reasons (e.g., existing personal commitments, health, work-life balance). ​Put Your Decision in Writing: If they continue to press the issue, send an email or letter formally declining the increase. State that your current contract specifies [insert number] hours and that you do not agree to vary these terms. ​Beware of "Fire and Rehire": In rare cases, an employer might threaten to terminate your current contract and offer a new one with the higher hours. This is a complex legal area with strict consultation rules—seek legal or advisory support immediately if this is mentioned. ​Get Free Professional Advice: Contact ACAS (Advisory, Conciliation and Arbitration Service) at 0300 123 1100 or your trade union representative for confidential guidance tailored to your exact situation.
And how does it then work in your office?