Tbh you sound similar to what happened to a mate of mine , he went a little bit further . Ended up with community service.
Just act the part when in court, have the "right attitude" etc.
If you can afford a good lawyer will always help , but unless you have loads of prior's or violent prior's , I personally wouldn't worry about it to much.
Unless you have some bad luck judge wise , but britain aint all that bad sentence wise sometimes. Even the worst case scenario's i've seen , people getting 4 years after getting caught with a massive setup.
Now you know they pulled that off atleast once,most probably they have did a few grow's to have a grow in that scale , not to many people jump in and start with several hundred lights/plants. and i'd bet they would be out in 2 year's.