Chris,
The wheel does not have to be removed, but it would help you to see what is happening. If you are not confident at touching the brakes best get someone along who has experience, although you will not find many who have seen a wheel cylinder of this type before.
I am assuming that you or someone, has been driving this Ferret recently? The cylinder is more than likely stuck, common problem as these vehicles stand around a lot. As you drive it, the heat from the dragging brake warms up the alloy cylinder and releasing it. When cold it is back to dragging again. Whatever you do, read the EMER (workshop manual) before attempting anything, so you understand what, how and why.
Richard