As per paragraph 2.5 of the Charities SORP, any GIft Aid claimed for restricted donations (ie. a donation for a specific purpose), is restricted to the same purpose.
Gift Aid claimed for donations made to a charity for general use, i.e. an unrestricted donation, is also unrestricted.
As unmatched donations made through Big Give campaigns after the target has been hit are unrestricted, any gift aid claimed on these donations is also unrestricted.