Confused! Pensioner

I took my annual bonus from the private company I worked for in shares. I retired in 1983. The company floated on the Stock Market in 1994 when I received my share certificates. I subsequently transferred some of my shares to my wife. They have now been sold and there is a capital gain. HMRC says I can us the share value as at 31st March 1982 but as they were first quoted in 1994 there was no share price in 1982. Do I used the float price in 1994 or the price when I transferred the shares to my wife to calculate the base cost or is there some other way to do this, please? Confused?