Hillman Gazelle

Use force in the right places to pull the Bakelite cap from the steering wheel.
It's held on by 4 lugs – 2 above & below the middle, and 2 towards the sides (by my thumb) :

You don't need to remove those 3 nylon nuts.  I did, so you can see those 3 Phillips head
screws, for which there are access holes – undo them and remove the horn ring assembly.
Don't drop the little spring washers on the screws like I did.  They can be difficult to find.

Use a 1 inch socket spanner to remove the main mounting nut.
Then you'll be able to pull the steering wheel from the spline.

During reassembly, use a 1/4 inch socket spanner to adjust the 3 nylon nuts, to give an
even fit and make the horn work – pushing the plate against the springs if you need to.
It's important that these nuts perform the function of electrical insulation.

Hillman Minx & Singer Gazelle Series I to IIIC

Loosen the 3 grub screws – almost to the point of removing them from their holes :

Pull the ring assembly out, and use pointy-nose pliers to pull out the electrical connector :

While you're there, adjust those 3 metallic 1/4 inch nuts so there's an
even clearance all around the electrical switch under spring tension.

Use a 1 1/8 inch socket spanner to remove the main mounting nut.
Then you'll be able to pull the steering wheel from the spline.