I agree with the previous comments: the temporary pursuit of non-damaging activities like amateur radio, an informal family game of cricket or sticking three pegs in the ground are examples of recreation. What matters is not what the gamekeeper says but what a judge would decide (as in the Dartmoor wild camping case). Obviously, you should remain polite and non-threatening in any conversation. But if you think you are in the right and the landowner or his/her agent continues to harass you, you should phone 101 for assistance unless they get violent in which case call 999.
The laws of England & Wales tend not to have long lists of Do’s and Don’t but rather have a general definition, e.g. recreational activities are allowed on CROW land, and leave to case law / common law to test the boundaries of that definition. Don’t expect to find a law saying it’s a right to set up an amateur radio station or to forbid it. The test of the “reasonable man” or probably reasonable person nowadays is expected. What matters: Is what I’m doing a recreational activity or not?
But as Tom @M1EYP said, in this case it wasn’t even about the activity, his beef was people on his land.
Not that old chestnut! That along with their new buzz word “conservation” is an excuse to get you off their land. ‘Disturbance’ of ground nesting birds by walkers is probably a third-order effect on their population. I refer you to a fuller science/evidence-based explanation of what factors really affect their numbers that I posted last time this came up …