I've had two bank staff jobs recently. Usually, the contract will be something along the lines of 'we have no obligation to offer you work, and you have no obligation to accept it'. So, you are entitled to turn down work offered to you if you can't manage it, within reason.
The downside is that your working hours, and income, will be inconsistent, and you may not get any hours sometimes. Plus, you may not have access to all the same things that permanent staff do (in one job, I wasn't allowed to view the shared staff calendar even though it would've made my life easier ), and being able to contribute to a pension may not be possible unless you're earning a significant amount.
Also if you're working just a couple hours here and there, and have to commute, the commute may actually eat up most of your earnings for the day (well, if your bank role is as low-paid as mine have been!!)
A company rang me in reply to my application and we had a good chat they were so lovely and the role sounded great. Unfortunately the shift patterns they offer just weren't feasible for me around my ex husbands shifts as we have children it will be so hard and confusing to sort childcare. So they rung me back after a while and offered me flexible hours as bank staff. It sounds perfect and I have my interview on Friday. Has anyone had any experience working bank hours? Is there anything I should be aware of and how do I go about telling tax credits what I'm earning and what hours I do ? Am I entitled to tell the company how many hours I'm willing to work ?