Ours is about 6%, do I win?
But you might as well ask for random numbers. Our house is smaller and in a poorer area than the average Mumsnetter could bear to live in.
Plus we are comparatively much better off than when we started out, are child free so don't need a big house and are too lazy and apathetic about the whole process to go to the effort of moving to a bigger/nicer house.
Percentages don't tell you much anyway. You'd have a lot harder time with a £500 pm mortgage on a £2k income than you would with a £2k mortgage on a £6k income because even though the percentage is higher, you've a lot more left over to live on.
Plus you have to consider what your other costs are - if you've little or nothing to pay out in childcare and commuting, that makes a big difference. Mortgages are often not a household's biggest expense.