AFAIK all land, no matter what its 'use' class, has standing agricultural permission. The council can never tell anybody not to grow a carrot, whether for own use or for sale. The same is true of keeping livestock. And livestock needs fencing; and again, there is no law against fencing (unless by way of an article 4 direction).
You cannot tell anybody to stop doing agriculture until and unless there is a nuisance ruling. That must come from the environment office, via, ultimately, a court order.
So you can tell the planning enforcement officer (who just want his desk cleared asap, and is happy to pretend he know what he is doing when has no legal training whatsoever) to jump in the nearest lake. Politely of course.
He will have come because of a complaint - planning folk don't come around unless someone make a planning complaint. So you could ask after the reasons that bought him there, if you wish. Yes, as others have said, ask for reasons in writing.
If the complainant now contacts the Environment office (under the same council) they will turn up, and you will have a issue not about the use, but about 'nuisance'.
-----
If and only if the planners could could consider your 'use' to be solely leisure then they would have a case for saying you have illegally taken land out of its designated agricultural 'use' and are using it for recreational purposes. So be sure to emphasise you are keeping bees for their yield, for home or sales, and/or raising bees for expansion or sale. Planners (and the Environment folk) are under strict instruction not to get in the way of growing businesses without very good reason, and you can use that to your advantage.
-----
However: if the land _use_ (the paddock you are in) has been officially changed from agriculture to leisure 'use' as a result of being used for recreational riding only, then you may find it has been changed to equestrian use ONLY. In that case you are on different ground, and I don't know what happens. There may be a court ruling that will help - if you can find it.
The request for detail should clarify the position. Planning enforcement officers won't generally volunteer _any_ information I've found. A written request goes to the legal team, and the response is legally stated.
If you wanted something to do while you wait, searching 'equestrian use, planning restrictions' or similar might throw up something interesting. Look closely at related planning appeals.
This offers a route into appropriate planning law in this area:
Agriculture Act 1947