I have arranged a Naturist visit to Glansevern Gardens, which are a few miles south of Welshpool. I visited the gardens for the first time, in the dead of winter when they were mostly dormant, but I think they will be quite stunning in the summer. There is also a lake which you can walk around. The cost is £7 a person, but please bring cash.
Picnics are not allowed anywhere in the gardens. There is a cafe (which you will need to be dressed to use), but understandably the opening of it is dependant on numbers, which can obviously vary a lot depending on the weather. I will be looking at options both to get the facility open, and to provide the owner with some certainty as to whether or not it will be worthwhile. I will update this entry accordingly, so please check here later.
Dogs on a lead are welcome, except in the cafe, but obviously you must clean up after them.
Here is a link to the gardens website http://www.glansevern.co.uk/index.html