Well, as I briefly mentioned earier, then you seem to be missing the big picture here.
Firstly, then it is completely irrelevant that you are currently living in a Listed building. It is perfectly possible to make and operate quite effective antennas, which are completely invisible and doesn't damage nor detract from the buildings exterior in any way.
The literal flagpole in the garden is just one example. Haul a copper wire up with the robe and done. Been there, done it twice myself (OK, strictly speaking one of those poles was actually an 8m girder mast, but you get the idea). If you are able to bury a reasonably effective system of ground radials in the lawn around the flagpole, then this can be an amazingly effective antenna below 30 MHz. However you usually needs the approval of your landlord, as your digging in the lawn will be visible at least temporarily.
Don't laugh at the clothes lines either. I knew a guy, who used exactly that as an invisible antenna. With the joints secured with good electrical connections those square clothes lines made from Aluminium makes for good antennas as a top loaded vertical between 14 and 30 MHz. Again provided you have a reasonable ground radial system.
Then there is the loft/crawl space directly below the roof. Done this myself once. Depending on what the roof is made of, then a dipole below the roof can be quite effective. Red brick works well here. However you frequently need the approval of your landlord to gain access to the loft space.
The proverbial random wire, made from thin, nearly invisible, enameled copper wire, and strung up using fishing line, can also be a very effective yet nearly invisible antenna when provided with a good ground system. Done this myself twice. If you need to gain access to the roof to put it up, then you may need the approval of your landlord.
Another option may be the small, temporary and possibly indoor antenna, which is put up when you need it. The magnetic loop is one example. Usually doesn't require landlord approval.
Secondly, if you *do* use an antenna like this for transmitting, then it is possible that, due to the proximity to the living space of your neighbours, your transmitter creates RFI in nearby electonics. If this happens, then your neighbours may not realize you are to blame, and it is likely your landlord is one of the first outsiders to hear about the problem.
Do you begin to see a pattern here?
Thirdly, there are such things as associations of landlords/people who rent out living space. They tend to cooperate on various issues of common interest, like how you manage your tenants.
Here in Denmark one of the problems we have had to fight for years are standardized contracts for tenants, which contains clauses against erecting antennas on the property.
The problem with your 'joke' is exactly the reason why it works: Your landlord knows absolutely nothing about antennas nor radio. Yet the next time, if it ever happens, that he hears about this issue from his 'colleagues', then he will remember the run in he had with you.
You see, you are not alone in doing what you did: Going for an outside antenna with all guns blazing from the get go. And make no mistake about it. From the point of view of your landlord that is *exactly* what you did.
Here in Denmark it has only taken a few bad apples, be it CB operators with illegal equipment or HAMs with zero sense of diplomacy, to have antennas banned as a standard clause in a significant part of the homes up for rent in the whole country. And once those clauses are in, it is an uphill battle to get them overturned. Even if you are on a very good footing with your landlord. Because he or she will likely know nothing about the subject, but if their colleagues recommend banning such an esoteric thing as antennas, then they must clearly be a very, very bad thing indeed.
Conversely, if you 'boil the frog slowly' and spend some time getting on the good side of people before bringing up the subject of antennas, then I am constantly amazed what you *can* get away with. Start with a small and inconspicuous setup, show there is no problem and work your way up from there. Assuming, that is, your landlord isn't predisposed against the subject in the first place due to the actions of people in other areas of your country.