I'm trying to replace a broken front wheel on a Mountfield M3 mower (an old
model, about 25 years old!), but - embarrassingly - can't quite see how to
remove the wheel.

I've removed the plastic "hubcap" but there are no visible fixings
underneath. However, behind the wheel is a metal plate with a pair of holes
in, through which I can see what appears to be the head of a pin passing
through the axle. I assume the wheel would slide off if this pin is
removed, but should the pin just push out, does it unscrew, or is some
special tool required?

Any help or advice would be much appreciated.

Chris