Grazing horses as you are is an agricultural operation. There are actually 6 different planning scenarios for horses but few people know the difference and quite honestly, with only 2 acres and no obvious commercial activity, then no one is going to care! In addition you have 28 days of permitted activities/year for which you don't need planning permission. So you, or anyone else you cared to invite, could actually camp for up to 14 weekends/year and it in no way alters the planning status and nor do you have to ask anyone's permission.