We're house hunting at the moment, looking around Waltham Forest and South East London, particularly around Lewisham council area. DW's parents live halfway around the world and visit for about 4-5 months every year to help out with childcare etc. We want to build a granny annex with a shower room and kitchenette in the garden of our new property. Are we dreaming in terms of getting planning permission for something like that in either of those boroughs?