However, I will say this - from a layman's point of view, it doesn't sound like harassment. It sounds like you are blowing things out of proportion. I understand your mental health issues are causing you to view things in this way, but the question is, will a judge see it in the same way?
The maintenance men entering your room - most of us would have just shrugged, said "give me a minute to get out of your way" and let him get on with it.
The cleaning lady bringing her dog in - presumably, she has brought the dog in before you were there, and it hasn't been a problem. She wasn't to know you would construe it as an attack. The dog may have just been being friendly and excited to see someone. Now, the landlord not doing anything about it *might* be a violation of H&S but did it happen again? Also, I would ask - rather than complain to the landlord, why not just have a word with the cleaning lady and explain to her politely that you have anxiety, are afraid of things rushing at you and not to bring it with her? And did it happen again?
The issues you have with other tenants - the one who closed the window, for example. He's as entitled to close the window as you are to open it. Have you considered that he might have considered you opening the window to be you harassing him? For all you know, he has hayfever and needs to keep the pollen out.
The mail redirect - again, for all you know, that could have been the postman, rather than another tenant. The scotch egg in the fridge - if it was that bad, why not just throw it out, rather than raise a complaint to the landlord?
From the landlord's point of view, you seem to have been raising a string of completely minor complaints over nothings. Obviously, from your perspective, things are rather different but if you are to bring it up before a court, they are entitled to ask whether the landlord has been reasonable.
The only thing you might have a valid complaint about is maintenance, but you would have to prove that a lack of maintenance either breached the terms of your agreement, or was illegal under the whatever the appropriate H&S laws are. And even then, you may well not be entitled to any kind of refund, as you accepted the condition of the building by remaining. It was an easy-in-easy-out lease, you could have left at any time if you were unhappy. Yes, I know you will say you had nowhere to go, but that's your problem, not the landlord's.
It sounds like a risk on your part to bring a case. I don't know what the law is, but if the judgment were to find against you, would you want to be found liable for their costs? It sounds to me like the landlord might have an equally valid claim against you for harassment of himself and other tenants.
Again - this is from a layman's perspective from the outside looking in. I am not offering any legal advice, just an opinion. Speak to a solicitor.
I am within my rights to feel perturbed at the maintenance man not knocking. Moreover, it was the LL's reaction to my reaction which bothered me.
Anyway I don't mean this to be the harrassment element per se.
The harrassment element primarily was that the rep told me over the phone that they had entered my room without my permission (l mentioned this in the OP). There was no context to it, other than my complaining that another tenant was shutting the hallway window right after l opened it. Saying that they had entered my room without my permission was provocation and l believe it was unflawful and could be construed as harrassment and l complained about it in email right after and that resulted in near total radio silence from the mgmt for ever more after that point.
I have a right to feel harrassed by it and it's certainly reasonable too. I didn't mention before, but the LL's rep would give me positively evil stares too, ever a deadly stare because l would never stand and chat, l would always be trying to walk away and l had already explained that they should expect this. Of course, l cannot quantify or prove a deadly stare, but it was there, always. I couldn't hope to bring that into my court claim though, obviously!
I never said the other tenant closing the window was harrassing me. However, each room had free electricity, the window was in the hallway, and he is always pushing the window open these days, in summer (and leaving it open overnight - one of my various complaints about maintenance - this invalidates building insurance, at least, MGMT's flippant attitude to my mentioning it). He does not have hay fever, the open window has very little impact on the temperature inside each room, l was opening the window to keep fresh air flowing, because the gents toilets - believe it or not - had windows that were painted shut, and had been that way for presumably years. That's right, if you took a poo, the smell would fill the building (but the female toilets had windows that would open), the only relief was to open the fire doors in the adjacent space, several walls away. So there was pretty good reason for that window to be open and l explained as much. There was also a health and safety aspect there, re: germs needing to be dissipated.
l believe it may have been that same tenant that was periodically leaving stacks of far right newsletters in the foyer, because they appeared around the time he would enter the building. The first time he saw me, he gave me a very evil stare in fact, so there was a bit more backstory, which l did not go into, nor shall l in court, as it is unfalsifiable.
The postman? No, it couldn't have been the postman. The postman could not access the lobby nor would have have any reason to put a mail redirect sticker on a piece of mail that was already in my pigeonhole. I didn't accidentally redirect another tenant's mail either, l ran the names of the ex-tenants and never-tenants whose mail l was about to redirect, by the LL's rep and they said l would be fine to redirect just those. In response, someone put my own redirect sticker on my own letter and left it in my own pigeonhole, and it only happened that once.
l'm intractable on the position that taken as a whole, there was some ill will out there, and the mgmt - this is the main thing - the mgmt were very nasty about it, as they were about any matter brought before them. Because they were just property investors, l feel. I don't believe they really wanted to do the LL thing, they just wanted babysitters for the building. Understandable, and the contract reflects this. But it spilled over into Negligence, Bad Service, and dareisay it, Harrassment.
By the way, anecdote: I once left a tube of bogroll in the toilet, and returned to find a note penned on it saying "Throw the toilet roll in the bin you lazy F@!# C@!#" fully spelled out. This l found to be genuinely heartwarming. So, l think l do feel context and l'm not just a pedantic ass about things.
As per the OP, some of these claims are more easily bolstered than others.
You say:
The only thing you might have a valid complaint about is maintenance, but you would have to prove that a lack of maintenance either breached the terms of your agreement, or was illegal under the whatever the appropriate H&S laws are. And even then, you may well not be entitled to any kind of refund, as you accepted the condition of the building by remaining. It was an easy-in-easy-out lease, you could have left at any time if you were unhappy. Yes, I know you will say you had nowhere to go, but that's your problem, not the landlord's.
I could not easily move and that's 99% of my present horror. One does not just move office!
I don't believe there are usually if ever expense claims in the small claims track.
I appreciate your kind hearted effort in cross examining me, that's after all what l asked for. I wish you well in life.
I guess this thread has run its course now ...

next step, free law workshop. Not everybody needs a lawyer, especially in small claims - thank God!