I believe the Minister and Transport for Wales have suggested we may in due course see tri-mode trains on this line, with both overhead electric, diesel and battery operation. How firm is that policy, because I'm aware that some concerns have been raised as to the added weight of the battery and, despite the advantage of that for coming through the Caerphilly tunnel, whether that added weight elsewhere in operation may make the trains overall less efficient? Not everyone is agreed that this is necessarily the right technical solution, given that we haven't really seen it elsewhere in the world.