Wherever possible charitable payments should be made under the Gift Aid scheme to ensure the maximum tax benefit is enjoyed by both the charity and you as the donee. This includes the flexibility in timing of the declaration which is available for a Gift Aid donation.
An election can be made to carry cash donations back to the previous tax year; both the donation and election must be made before your Tax Return is submitted and before 31 January following the end of the tax year.
Donating to charity an asset (land or quoted shares) that has a potential Capital Gains Tax (CGT) liability can save CGT as well as obtain Gift Aid relief. There is no carry back facility for non-cash gifts.