“the defence must have a proper evidential basis for asserting that any such previous statement was (a) made and (b) untrue. If those requirements are not met, then the questions would not be about lies but would be ‘about [the] sexual behaviour of the complainant’ within the meaning of section 41(1). The judge is entitled to seek assurances from the defence that it has a proper basis for asserting that the statement was made and was untrue.”