Go for making a regular breakfast vegan--chances are vegans might just want a proper English fry-up (which of course I realise isn't anywhere near as nice as some of the other recipes being suggested). I find that mushrooms, fried tomatoes, bubble and squeak (if they do that in Cumbria), baked beans, and fried bread make for a substantial breakfast.
It's easy to make breakfast like this for everybody, too--the key is to go for vegan fats (i.e., Pure or Biona or Suma margarine or oil). If they want, they can also add processed vegan things like sausages or burgers--they'll more than adequately substitute for any meaty additions. Redwood Foods' VegiDeli range has lots to choose from:
+1 for this suggestion