Scotland Bill

Before the noble and learned Lord leaves that point about two different jurisdictions, can he perhaps clear up for me the difference in relation to corroboration between Scotland and England? As I understand it, at the moment, because we have UK traffic legislation, only one policeman is required to provide evidence in an arrest. However, were Scottish legislation to apply and there was a different alcohol or speed limit, would that be subject to a different form of corroboration, since it came from Scots law rather than UK law?