If you pay tax, all your donations to the Society qualify for Gift Aid and the Sons of the Rock Society can recover the related tax. As a tax payer you must pay an amount of income and/or capital gains tax at least equal to the tax that the Society would reclaim on your donations in each tax year. (If you give £25, the Society can currently recover £7.05). A declaration can cover all future donations as long as you are paying sufficient tax or until you cancel the declaration.
I want the Sons of the Rock Society to treat all donations I make from the date of this declaration, until I notify you otherwise, as Gift Aid donations.