You must be a UK taxpayer and have paid as much income and or capital gains tax (or more) as the 25% of your donation that we are getting back (28% until 5 April 2008).
You cannot give Gift Aid consent if you are a participant in a sponsored event for which the charity has borne some or all of the cost, or if you are connected to the participant. (A "connected person" is a wife or husband, a relative - brother, sister, ancestor - e.g. mother - or lineal descendant - e.g. grandson-, the wife or husband of a relative or a company under the control of the participant or connected person).