As a Chartered Accountant the present rules are :-
If you own an Aim share and sell between 1 & 2 years of buying the gain is reduced by 25% which then subject to CGT tax at your highest rate of tax, which if 40% would equate to the gain being taxed at 30%
If you own an Aim share and sell after 2 years the gain is reduced by 50%
which is then subject to CGT at your highest rate of tax, which if 40% would
equate to the gain being taxed at 10% overall.
Both the above ignore that you are entitled to your annual CGT excemption