There are several steps to the calculaton
1. Deduct the cost from the proceeds. If the property was held at March 1982 the cost will be the value at that date. This is your gross gain.
2. Deduct the costs of purchase (including stamp duty) and sale from the gross gain.
3. Deduct the cost of any improvements made to the property (not repairs)
4. Deduct an allowance for inflation from the date of purchase until March 1998. To do this, multiply the cost (or March 82 value) by the relevant percentage on this table
http://www.hmrc.gov.uk/rates/cgt.htm
5. Deduct a percentage of the gain you have now calculated, for taper relief - see this table to obtain the percentage
http://www.is4profit.com/is4money/tax/taperrel ief/index.htm
You now have a net gain.
You have an annual capital gains Tax exemption of �8500, which will be available if not used elsewhere. Assuming this is available, you deduct it, and are left with a taxable gain, which is taxed as the highest slice of your income for the tax year.
If you have ever lived in the property as your main residence, the gain may be drastically reduced, and there are several further steps to the computation.