Contract advice.

If they believe you have breached your lease terms then they need to notify you in writing and a breach normally brings a lease to an early end. You should discuss with your solicitor who is advising you the best time to serve them notice to quit and your obligations under the lease so everthing is in order at the time you need to leave.

First, all landlord/tenant issues should be dealt with formally and in writing. There is no such thing as an informal relationship in commercial lettings.

Secondly, you say you are a subtenant not a tenant so your landlord presumbly is the tenant and has at least one landlord superior to it? If that is the case then your landlord is governed by the terms of its lease and can't just do what it wants in the building.

Dealing with your specific points:
1. "I have had some problems with my landlords regarding legal fees about setting up the sub-tenant contract. My solicitor said that it was negotiable with the landlords as the wording in my contract is disputable but they will not budge over it"

It is common practice to agree who pays whose fees at the outset, before solicitors get involved. Presumably superior landlord's legal fees were payable apart from LL and T's fees. If your contract / heads of terms did not spell this out then you are not responsible for this. If your solicitor says the contract is ambiguous then it is his fault for not agreeing it clearly and you should pursue your solicitor if you ended up paying fees you hadn't agreed to.

2. "They do not talk to me, which as they have to come upstairs to the toilets is difficult".

You can't force people to talk to one another. Don't let this get to you!

3. "they have taken all my signs down from the door downstairs so basically nobody knows we are here "

You are not permitted to put up any signs unless your lease says so. Again, if you wanted to put up signage then this should have been negotiated and put in the lease. It is possible that your signs require superior LL's consent in which case you have to apply for this to your LL formally and pay the costs involved in producing a licence for alterations permitting them. There may also be planning restrictions.

4. "they are meant to be replacing the windows due to H&S but they haven't"

Does it say this in your contract? If not then they don't have any obligation to do this. It depends on what it says in the lease. Again, if it does, then you need to write to them pointing out the clause in the lease you are relying on in relation to repairs or replacements.

5. "so I have not been able to put signs on the windows"

This is not your right unless specified in the lease.

6. "I am getting myself prepared for when I have to tell them I am not staying as I feel that it will be more difficult."

This is a commercial decision and there is no need to worry about it! You will need to follow the correct procedure though in giving notice. Again consult your lease and your solicitor.

7. "I feel that they will try to say that I have breached my contract, for these reasons"

Do you have a break clause which can only be exercised if you have not breached your lease? This usually applies only to non payment of monies due. If you have breached your lease they will take action so you don't need to worry about it.

8. "I asked them last year if someone could come into my business and provide another service on a fee-sharing basis which they agreed to as in my contract it should not be unreasonably withheld. Unfortunatey my contract says that they have to put it in writing which they haven't and I have not asked for it either, as we were at the time being friendly. Also they think that a colleague in the same line of business as me, who works with me and is also fee-sharing is paying rent, which he is not.

If you want to share your premises you must apply in writing for a licence to sublet/share. If you haven't followed the procedure, that is your fault. I don't understand what the problem is.

9. " I also do not want the hassle of any problems or court action after I leave, I just want to move on."

If you have paid all monies due, served all the correct notices to vacate, not carried out any unauthorised alterations, not sublet without consent and leave the premises in the condition specified in the lease (regardless of the state they were in when you moved in) then there is nothing to worry about.

I can't see what the problem is from what you have posted. I recommend that you sit down and read your lease carefully.

If you have any actual problems then please post them and I will try to help.

I have to agree with Deniser im afraid.
I used to work in property management myself and have dealt with a lot of commercial leases. It sounds to me like you are one of the worst possible tenants any landlord should have and if I were your landlord I would try to get you out as soon as possible before things get much worse. At the end of the day you are leasing a part of a property which doesnt belong to you and it is at the sole discretion of your landlords to decide what goes on and what doesn't. Dont make life difficult for yourself by disputing everything in your lease and bothering your landlord about new windows etc. I bet you didnt say anything about the condition of them when you signed the lease!!