“suddenly you're suggesting four days a week now.... let's get this straight, you need to keep a diary of these things”
Just want to put the stress on my original post, where I stated “It was ok for me until he started to spend 3 days and nights in a week in the property”.
It is not suddenly, in average it is three days and three nights, whereas the maximum is 5 and the minimum is 2. Yes, I am keeping the diary since January 2009. Last year he didn’t stay over night at all, but last week for instance he spent 5 nights. Still not a resident?
“your friends are likely to be people you know less well than she knows her boyfriend” – true, but at the same time they have not used the shower here and usually I prepare tea and coffee myself, and they have not walked in the on the kitchen in night-suits.
And finally, he has or had a key. I could not check his pockets. He was able to enter the premises when she was not inside.

thanks for the replies.
To Alicepalace
It is true that English is not my first language. Did it look like that I was kidding somebody putting my concern on the forum and asking for your help and advices?
As you noted “I don't really understand the safety issue... What would your ideal outcome of this be, then?”
My outcome is to follow the rules written in the Tenancy Agreement. If the Tenancy Agreement states that nobody except people mentioned in the contract can reside in the premises, it means that there is a breach of the contract. You can try to solve the problem by speaking to the other tenants and provide at least the
It’s all about the risks. When I said it was fine for me before, I meant, that up to certain point you can leave with those risks. When somebody visits (Visit not live) you flatmate it’s fine. But when you have to stay in one apartment with somebody you do not know for three/four days in a week and the doors to your room are open, then you definitely can’t say that you are in a safe place. The other issue, is that her boyfriend now have a key form the flat. According to the contract nobody can keep the keys except the tenants. Is it still ok? Definitely not for me. I used to live according to the rules and if I’ve signed something, I would not have to breach the rules. Certainly there are always such situations, when you have to come to the agreement with whom you have this conflict. Unfortunately we didn’t.

Alicepalace, excuse me my curiosity, how many languages do you know?

I am a part of a student community (PhD in particular), therefore I wanted to share with you my worry. Most of the replies were really useful and I’ll follow you advices. Sure, that a lot people from here appeared in a situation like this from one side or another. And perhaps some of you may face these problems in the future.

Thanks everybody for your support.
Donzy
That’s a good idea to invite my friends as a reaction to unfair behaviour of my flatmate. Then she will invite her, then I’ll invite strangers from the street… etc. Is it not a “war”?
I have friends and from time to time we have parties in my place as well. It’s normal I think. Same my flatmate does. She invites her friends either.
The problem here is that one person supposed not to live in a flat in fact resides in the premises.

Phdbug
I have very positive experience of living in the Uni shared accommodation. I lived in such accommodation at the first year of my PhD. I really enjoyed that time – 4 of us shared kitchen. Unfortunately we are not allowed to stay in the Uni Halls after one-year period of staying. I think it’s not only the case with the postgraduate students. Therefore I had to move into the private accommodation. Taking into account my previous positive experience of sharing although I must say it’s totally different for me in this case.
What just have come to my mind, at the Halls of residence you could lock your door when you were inside your room, whereas here we do not have any locks (except the entrance door), maybe that’s why I fill myself unsafe with “strangers” inside the flat.

Thanks Bettyspaghetti.
I did almost everything, you've mentioned in your post: I've tried to speak to her and then both of them several times and tried to talk about bill sharing. What they said, he does not live there (not a resident of the property), therefore he would not contribute to the payments for electricity, internet, water etc. I do not want to pay for her boyfriend, but in fact I do.
I have not mentioned in my original post that Landlord stated to move out I have to cover the costs of his Agent - 570 pounds for finding somebody to replace me and to make the credit check. Although I said I would find the tenant myself, he told me would have to pay that amount of money without any reductions.

Satchi
Thanks you for advices. Probably I'll write a letter with the explanations why I want to leave and send it to the Landlord, both by post and e-mail. I'll mention that the deposit will be left for him and that all bills from my side have been paid.
I’ll see what he will reply. I think I’ll share updated information with you.

Hi everybody
I am a PhD student, however my question is not related to studying so much. I live in a shared accommodation. It’s a two double room flat. I am sharing with other person. The Tenancy agreement which we signed was between us as the tenants and the Landlord. My flatmate is a nice girl, however I have fundamental disagreement. The thing is that her boyfriend started to come to the property. It was ok for me until he started to spend 3 days and nights in a week in the property, and even sometimes when she is in the college, I can see her boyfriend making coffee on our kitchen. In the contract we have only two tenants, therefore I’ve asked him to leave the property, however he was very hostile to me. I’ve tried several times to speak with both of them about the agreement and that it is not legal and not fair to me either, because the bills are split into two, instead of three. I’ve reported about that to the Landlord, but he said it is not his business and we have to come to the agreement with the other tenant and her boyfriend. Now I am feeling myself not safe there. I decided to move out, but the Landlord does not want to permit me to do so, because the end of the Tenancy Agreement is in July.
Can you please advice me something what to do in this situation. Should I move out without Landlord’s permission and leave him my deposit? Or this may cause the other problems with the Landlord and may go to the court and start the process against me?
Thanks.