Mr Piggott's biography of Stukeley's good. As for Lethbridge, get Colin Wilson's book Mysteries, which has a very good & very lengthy overview of the fella. You could get Tom Graves' Essential T.C. Lethbridge, but it aint as good as Wilson's overview (he curiously left in some of Lethbridge's 'Legends of the Sons of God' material, which he shouldn't have really).