There is that.
||If you look it up on the internet so you know what the rules are, you could then go to your planning authority with the information if needed. When we went to them over an idea we had we were told we couldn't put up anything, whereas the rules said we could under agricultural regulations and temporary buildings were exempt anyway.|
||I think the biggest issue is using agricultural land.|
In most instances they come under permitted development AFAIA.
That means you don't need planning permission, submit detailed plans etc, but still need to notify them. If they don't object within a certain period you can go ahead.
Personally if you just want a tunnel for growing for your own consumption I would just go ahead & not say anything.
If it's to be part of a business might be best to go down the official route.