If you got free shares in your employer's company, from your employer, and now plan to sell them, is it simply a case of 20% CGT on the total sale value??
Unless you got the shares through an approved profit sharing scheme you are liable to income tax on the value of the shares when you receive them ,then cgt on the gain since then
This topic and the one that it links to might also be of interest in relation to the income and CGT tax treatment of such free/discounted share schemes. AS Capall hints at check if your scheme is a Revenue approved scheme in which case the tax treatment may be different to the "usual" income tax on market value less discounted (option) acqusition price and CGT on disposal price less market value at time of exercise/acquisition.