Gift Aid provides Tring u3a with additional income at no extra cost to you. Making a Gift Aid declaration does not affect you in any way. It doesn't mean you'll need to make a tax return (though, if you're a higher rate tax payer you can claim additional tax relief by including your Gift Aid donations on your tax returns).
Gift Aid will be claimed on the membership fee above and secures membership of Tring u3a only and does not secure rights to personal use of any facilities or services provided by Tring u3a.