if you have money in a share ISA you dont need to worry about CGT ever, your protected, it can go up as much as you like. The CGT allowance of 8.2k applies to investments outside of your ISAs...
You can open/add £3000 in a cash ISA and £4000 in a stocks a shares ISA each tax year... ie 7k tax protected investment each year. If you need to investment more than 4k pa in stocks and shares, you can but if the sum of your investments (excluding your primary property) rises by more than 8.2k in a year your liable for capital gains on the remainder (I think, its a little complicated)... Basically dont worry unless your loaded... Interestinlgy second property, BTL, cars, anything, Art?, is also liable for CTG.
Oh added disclaimer check everything yourself, im not giving you any financial advice its just idle chat