Aha. Thanks folks - white sauce on top only, more pasta layers. Will report back! (Could be some time, I make a big 'un when I do one and we're still eating the current one. The meat is venison mince with leftover home-cured gammon and it is absolutely scrumptious. Just looks dreadful!)
And Simon O, over the years I have tried it both ways, pre-cooking the lasagne sheets and not. This last one was not pre-cooking the sheets.