Can you be forced to carry out management duties at work when you are not employed as a manager?

Nobody can be 'forced' to do anything at work. If you are asked to do something you don't want to do, you can decide not to comply, but you should promptly explain your reasons. Even if you are being unreasonable, you can't be 'forced' - there are many options available to you and one of them is to leave that employment and find another job.

On the other hand, if you are not a manager and yet you are asked to do management duties, you might see that as a great opportunity which you want to take up. However, before agreeing, you should ask yourself why existing managers are not doing these duties themselves and what benefits you will accrue by doing these duties yourself.