hi donna, good link there, which basically says they cant make you do anything unsafe. However, how a 10 hour shift is unsafe, or bending, or lifting or sitting on the floor is unsafe is beyond me.
I don't think it's unreasonable for them to expect you to continue with these duties for as long as you can comfortably do them. When you are very preg it might be difficult for you to lift safely because you wont be able to take the weight near your body, as the bump will get in the way. It might become hard for you to get up if you are sitting on the floor, and at that point it would be silly of them to expect you to do it.
the employer should carry out a risk assessment with you to identify the parts of your job that will become more risky