So, just to check I'm reading it right - you have 2 acres of land, but when you applied for your holding number you didn't submit a map outlining the land connected to the holding - so the holding number only covers the house and curtilage? If that's right, you can just add the 'new' land to your existing holding, it should be a simple process.
I think your asking if you have any permitted development rights as its agricultural? My understanding is that because of the relatively small amount of land you have you'll have to go through the normal planning process. You could look at building a 'garage' to the max size allowed without planning permission, and use it for storage when not filled with cars..