If an inspector calls...
...there are steps that you should take to protect yourself, even if you are certain that you do not require a licence. The following measures may sound like you are becoming a conspiracy theorist but they are prudent, just in case. Inspectors are understood to receive a bounty upon conviction; there is a financial incentive to prosecute.
There is no legal requirement to admit an inspector, unless he has a warrant. However, these pages are written from the perspective that you have nothing to hide. Nevertheless, your first decision should be... do I let him in? Inspectors are well trained and skilled in their craft and may therefore try to trip you up. There is absolutely no legal requirement to tell an inspector why you are not admitting him... even if he asks. In fact, you do not have to answer at all any questions posed by him.
If you decide to let the inspector in, he should show his official identity. Insist on corroboratory identification such as a driving licence. Make a note of the inspector's name, address and any other details. While he remains outside, telephone the TV licensing centre's number on his identity card for verification. You may even like to photograph them, if you can. All this guards against bogus con-artists who masquerade as inspectors with a view to burglary at some later point - yes, it has happened.
Get a witness - a neighbour perhaps - before admitting or even talking to an inspector. Introduce your witness to the inspector and tell him why the witness is present... to observe the meeting and installation with you both.
If the inspector believes that you are using equipment unlawfully, he will undoubtedly try to conduct a formal interview, under caution. Remember that you do not need to answer his questions and you can demand that he leaves at any time.
Do not sign anything, even if it seems innocent. There are plenty of accounts of how TV licensing misrepresents.
Keep accurate notes of the meeting.
Tell the inspector that you do not expect any further visits.
These steps in themselves do not guarantee you will escape prosecution. Remember that you are actually deemed to be guilty till proven innocent!