Tax benefits of an ISA?
You pay no tax on any of the returns/growth you receive from your investments held in an ISA. This includes dividends, interest and bonuses, but an ISA investor cannot claim the tax credit, which is attached to a dividend.
You pay no tax on capital gains arising on your ISA investments (losses on ISA investments cannot be used for Capital Gains Tax purposes against capital gains outside your ISA).
You do not have to declare income and capital gains from ISA savings and investments or even tell your tax office that you have an ISA.