Eek, Sorry for the length! Employees are given the right to request flexible working, employers must process and assess each request however they may decline based on very clearly established criteria. Eg detriment on other employees, financial burden, negative impact on customers, inability to cover an employee's absence.
They may change an existing arrangement if they can strongly argue the original grounds for acceptance are no longer applicable. Any change to the fwa needs to have gone through a thorough phase of negotiation, if they have failed to consult meaningfully they risk possible claim to breach of contract, but it's a long arduous expensive route through Tribunal, so they may be willing to risk the employee not having deep pockets.
i know my new manager didn't like me having different shift than the rest of the office and I think he has been trying to find and "excuse" or reason to change my shifts
Your manager must have a more robust case than doing this on a whim and some vague reason that he wants everyone doing the same shift times. That isn't in the spirit of flexible working. The government put it in place primarily to support families where both parents are working, and having to juggle childcare, and your manager is pushing for a one size fits all but so far not quantifying how your fwa will negatively impact the team.
You need to go into the grievance meeting fully prepared with a business case to show:
- How your 9 year history of fwa has never impacted your performance or delivery to objectives.
- Why you believe that it does not impact negatively on customers giving examples of the great service you provide.
- Emphasis that your fwa is in place to support the needs of your young family, and by removing it they are effectively taking away your livelihood and income because you DH is also doing shifts and their proposal make it untenable for you.
Don't say it in so many words but HR may well look at point 3 and interpret that as potential for a discrimination claim. Sometimes it's effective to feed a few hints like that and let them draw their conclusions
. The most powerful argument is your service history and precedent of your fwa. A colleague of mine put forward the above argument and they backed down.