Neil,
The ignition switch is on top of the column under the dash. You don't have to pull the steering wheel. But when reinstalling the switch needs to be 'timed' to work correctly.
Loosen the bracket holding the column to the underside of the dash, remove the headlamp dimmer switch and then the ignition switch. When re-installing do NOT install the dimmer switch at the same time, it makes it harder to get the ignition switch timed.
Instead, put the two capscrews that retain the ignition switch in finger tight, then actuate the key and make sure you have both a sprung "start' position and an accesory position energizing correctly. Tighten down the capscrews and re-check. When it is all timed up, remove only the one screw necsssary to install the dimmer switch, leave the other screw tight so the timing won't get out of whack.
It sounds tougher than it is, the worse part is laying on your back trying to get your hands and arms under the dash. If you don't have them now, purchase some small combination ignition wrenches, the capscrews have either a 9/32nd or smaller head size.
Good Luck,
Tom