There was an article these days mentioning that the Middleton's have sought permission to build an additional "granny's flat" and a home office as annexe to their garage. I thought on reading that that this is probably to house the security officers of William and Catherine during their stays with Catherine's parents - but now I could imagine it is to house the Middleton's security staff or at least a gardener's lodgings where someone lives who is employed to take care of gardening and "receives" such uninvited visitors.