I looked on Ebay and found KR Classics (Roger and Kim Chaplin 01622 862149, rrogchaplin@aol.com) who import and supply excellent quality covers at many classic car shows and have good feedback.
The cover arrived (eventually, as the size I needed was out of stock at the time) with full instructions and everything you needed to fit it.
Here's how it was fitted:
First the wheel was cleaned thoroughly with warm water and mild detergent (washing up liquid
Then I stretched the cover over the steering wheel and adjusted its position. Placing the seam at the bottom probably looks best - as suggested in the instructions, but if you own a rallye car you might want it at the top.
The finished product really does look and feel excellent IMHO. I took it for a little test drive in the country just to make sure. Perfect! Cheers
Karl