The circumstances of the property being connected with a bond make this a little uncertain but I shall give you figures as if you owned the property outside of a bond arrangement.
Between March 1982 and March 1998, indexation allowance was used to reduce gains. This was an inflation allowance. The rates are here
. The rate applied was determined by the purchase and disposal dates. As I don't know the purchase date or the disposal date I'll leave indexation allowance out.
Another complication is the date of disposal as the CGT regime changed between 1987/88 (6 April 1987 to 5 April 1988) and 1988/89 (6 April 1988 to 5 April 1989) as you will read here
. Prior to 1988/89, the CGT rate was a flat 30%. From 1988/89, the taxable gain was added to income and charged at the income tax rates applying. In 1988/89, the income tax rates were 25% and 40% so the highest the CGT could be charged at was 40%. The date of exchange of contracts is the critical date for CGT in most property transaction cases.
If the disposal occurred in 1987/88, the first £6,600 of the gain would have been exempt. The balance would have been charged to CGT at 30% so on a gain of £300,000, the CGT charge would be £88,020 (£300,000 - £6,600 x 30%).
If the disposal occurred in 1988/89, the first £5,000 of the gain would have been exempt. The balance would have been charged to CGT at 25% and 40% but if we assume your income exceeded the 25% tax band and use 40%, the CGT charge would be £118,000 (£300,000 - £5,000 x 40%).
As I said above, I have ignored indexation allowance which would reduce the taxable gain.