Wait, what? Can you chose not to use a height-adjustable desk, and your employer is only responsible for offering you one, or are you 100% forced into using a height adjustable desk?

For work you must use a height adjustable desk. It doesn't have to be electric, you just need to be able to adjust it to your correct work height. If you don't use it, and I don't know work at your kitchen desk, that's technically a violation of workspace rules. Your boss tell you to use a proper desk, because if they don't they can be fined.

You also can't use the keyboard and trackpad on your laptop. You must be provided with a separate keyboard, mouse/trackpad/trackball and a monitor. Working on your laptop is for emergencies or very brief tasks.