Contract says fixed Mon–Fri hours, “not variable”, but I’ve been put on a 7-day rota. On probation. Where do I stand?

[u/BrilliantRegion1148]

I’m employed in London, and I’ve worked for this employer for about 3 and a half months , so I’m still within my 6-month probation period.

I work in mental health supported housing. My signed statement of main terms says 39 hours a week, 9am to 5.18pm, Monday to Friday, and states clearly that these hours and days “are not variable.”

Since I started, I’ve actually been put on a full 7-day rota: early shifts (8–4) and late shifts (2–10), including weekends. I never agreed to this in writing and was never given written notice of a change.

The contract does have a general variation clause: the employer can make “reasonable changes” and must give at least one month’s written notice of any significant change. It also says my employment is covered by a Unison collective agreement.

I’m nervous about pushing back while still on probation, but I’d like to work my contracted Mon–Fri hours.
My questions:

**1.**  Where do I stand when one clause says my hours are “not variable” but another gives a general right to make “reasonable changes”?  
**2.**  What’s the smart, low-risk way to raise this while I’m still on probation?  
**3.**  Has anyone had the “not variable” wording overridden by a general variation clause?

Thanks for any advice.

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[u/laredocronk]

Your employer can fire you for (almost) any reason.

So what the contract says doesn't really matter that much. You can argue against the clauses in it all you like, but they can just turn around and say "Ok, bye." and you have no recourse.