Hi Potter
I saw your post and I'm new here too, came here today with the same question in mind so I thought I'd say hi in solidarity. The planning issues seem to be a minefield when you're considering investing. I've found a perfect piece of land for my purposes - one acre market garden plus a couple of acres for a community-managed forest garden - and it's up for auction tonight. I have the cash to buy it but if planners choose to be difficult my project fails and I'll have wasted thousands on auctioneer and legal fees. Here's what I've learned from research. Please assume I'm wrong though, you'll need to do your own research or ask an expert.
The good:
- market gardening is the same as agricultural use as you're producing food. (I think this may also be true if you're growing cut flowers but I've not looked closely at that.) So you shouldn't need permission for "change of use"
- there are some "permitted development" rights for sites between 0.4 (just less than an acre) and 5 hectares that say what you can do without permission but new buildings aren't included. That's not to say you can't build but you will need planning permission
The bad
- The main problem is the power of the planning process, grey areas around planning permission and the apparent arbitrariness of planning decisions
- You'll find various guidance and some legislation but lots seems to come down to case law and planners' power to apply law according to local circumstance
- You cannot assume that you would not need planning permission for sheds, polytunnels, produce preparation and storage etc. You may wish to assert that your structures are temporary and therefore not "buildings" but it's a matter of planners' power to interpret.
In my case I've also got a seller who's included an "overage" clause in the contract. If my auction bid is successful they'll have a right to claim 30% of any increase in the value of the land if I get planning permission for "development" and they'd be due the cash as soon as the permission is granted, as far as I can tell. While use of buildings for agricultural use is apparently exempt I'd still have to tell them if I got permission for a polytunnel and tool store and hope they (or their successors) didn't insist on a costly survey, legal fees and extra cash if they win in court. And all I want to do is earn a little money growing fruit and veg and work with the community to conserve the environment.