Sorry OP for only reading the whole of the first page, I couldn't stomach the harassment that you were getting from most of the pp's, so I have only read your replys all the way through. Please read mine to the end if you can face the length of it, as I am afraid that it will be very long!
I do think that you (your DH) should be fined for smoking in the room, but I also think that an establishment should have to have it written down in every bedroom what the fine is for breaking the law about smoking inside a commercial establishment. I don't know if owners can set their own charge according to what costs are involved, or even if the only way to legally fine you is for them to apply to a court, and a judge decide what you must pay. I presume that this landlord would not wish to go down that particular route.
My reaction to his demand for you to pay a £150 fine would be something like this:
"Dear Mr ...........
I very sorry that you are under the impression that someone smoked in our room overnight. My husband is a smoker, so I think it is quite likely that his hair, body, and clothes left a smell of smoke in the room. As a non-smoker myself I know that before I met my DH, but met up with people who were smokers, I always had to have a shower straight away when I got home, and put my clothes straight into the wash, as both I and my clothes would stink of the horrible smoke, and I didn't want to transfer it to my furniture and linen.
I think that you need to not allow smokers into your establishment at all, not just insist that they don't smoke inside it. Otherwise you will inevitably blame innocent people of smoking when they haven't.
I now regrettably have to give you my invoice for a very unpleasant stay in an establishment that did not advertise it's rooms honestly. When I booked my husband's and my room, it was advertised as being a luxury Kingsize, but it was not. The bed was not a Kingsize bed, the room was certainly not of the size or standard of a luxury Kingsize room. I also do not understand how you could consider the en-suite as anything more than a cupboard. The toilet, shower and sink were so squeezed in, that had I wished to disrobe in there I could not have managed it, unless I was a contortionist, which sadly I am not. My husband could not get comfortable in the bed overnight as it was not big enough for him.
Even though we mainly had a miserable stay - I will remind you of our treatment at your hands soon - I did not complain at the time as life throws us these curve balls, and I didn't want to cause myself any more stress than I had already been through with you. Also, being aware that we have all as a country, in fact as a world, been through a horrendous time in the last 18 to 20 months, I was trying to give your terrible attitude towards both me and my husband the benefit of the doubt. I now see that I should not have given you such a leeway, as you are a professional business man who relies on the general public for your service industry business to survive. So, at the very least you should be pleasant and polite to all your customers, or at least until they are rude to you. You were not at all pleasant or polite to us...."
[at this juncture OP please write down all the salient points you told us, including him complaining about how much Prosecco you ordered, because as you have already quite rightly pointed out, it is up to the landlord to refuse to serve someone if their behaviour shows that they have drunk more than their body can happily cope with]
You should then tell the Landlord that you expect your original fee for your room to be refunded, as it was definitely not as advertised, which meant your husband could not get a good night's sleep (circa £85 I think you said).
Then you tell him the figure that you expect in compensation for having had your long anticipated night away totally ruined by his horrible behaviour. I think that figure should include your travelling expenses, and say about £70 for the upset he caused you and your husband. So even without the travel expenses you expect a figure of £155 from him to be in your bank by the end of the week.
Of course he won't pay it OP, but hopefully he will drop his claim for £150 from you. Either way, until you get a court order telling you that you do have to pay him that money (and I don't think for one minute that it will come to that) then please don't pay him a penny.
Lastly (and thank you if you have stayed with me this far OP), if the landlord had been lovely, and if your bedroom had been what you were led to expect, my answer to you would have been to accept an itemised fine from him, if the costs seem reasonable, and ask your husband to apologise for his very unreasonable behaviour in smoking in the room. I am so sorry that you had such a shitty time OP, one to clock up to experience I am afraid, and hopefully your DH in the future will follow any reasonable, and/or legal regulations of an establishment he is visiting. 💐💐💐