Legislation in respect to what aspect of gifts exactly? It's difficult to understand what you're looking for from your post. There is no legislation that expressly permits or prohibits gifts, it's simply an aspect of owning property that one can gift it away.
If you're interested in the taxation of gifts then that is covered mainly by the IHT Act 1986 - as to gifts to individuals look at the rules on 'potentially exempt transfers', as to certain tax-exempt gifts look at ss 18 et seq.