Bigger hammer was in fact the answer. A little white grease and some persuading. Not sure its ever coming off but hopefully it doesnt have to. 

805minis, use a bigger hammer!
I agree with 6464s.
Martin.

I've been working on a 92 mini. I removed the OEM steering wheel and counted the splines- 48 x 3/4 inch. I just bought a MOMO hub which fits perfectly.

Does anyone know the actual count and size of the Steering wheel hub splines, and which cars are and are not the same? Trying to fit a new wheel on a 1971 MK3. As far as I know the column is original to the car. The wheel in it is the big ol original 2 spoke wheel, horn button on the indicator stalk, but otherwise looks the same as the original MK1 wheel. I assumed a MK1 steering wheel boss would fit, but it doesn't seem to. I have a box of steering wheel bosses, some fit, some don't. The only ones that do fit are big bulky ones that look silly with the slim early steering column cowl. Im finding conflicting information as to what "should" fit, though most of what im finding says all steering wheel bosses are the same up until the 96 MPi. As far as I can measure it is 48 spline x 3/4 or 19mm? do I just have a bunch of inferior quality steering wheel bosses?