I let my friend stay with me as she was in trouble. Things have dragged on and her behavior has been out of line, (damaging things, never cleaning up after herself, taking drugs)
I have asked her to move out but she is refusing to claiming she has tenancy rights when she has never signed a tenancy agreement or paid rent,
I have decided to change the locks and she is claiming that she can report me to the police.

What legal rights do I have to do in the situation?

Own? Rent?
Either way, if her name is NOT on the paperwork... my "guess" is she has NO rights. Its not her place.

Well first stop referring to her as a friend. She is no friend if she is doing this to you.

You don't say how long she has been there, but its very probable she is right. It doesn't take much for a person to establish tenancy. Getting mail at the address is usually sufficient. A written or even an oral lease is not required, nor is payment of rent.

As a tenant, she needs to be formally evicted. Since there was no agreement to pay rent, you probably can't serve her with a pay or quit. Since there is no lease, you would have to check your local laws to determine what the minimum notice is that you can give her. There is a sticky at the top of this forum that leads to local laws.

If she hasn't vacated by the deadline, you file in court for an eviction order. Once that is granted, if she still refuses to move, you can have a sheriff forcibly remove her. THEN AND ONLY THEN can you change the locks.

OK so she's left, taken her things and stolen the keys, I wouldn't put it past her to come back when she knows I'm at work and do some damage.
I now have to pay £160 to get the locks changed, and I have to report it to the building owners to get the front door of the apartment building locks changed and I'll have to pay for everyone in the building to have their keys changed for the main door.
Can I press charges for this, is it classed as theft?

ok so shes left, taken her things and stolen the keys, I wouldn't put it past her to come back when she knows I'm at work and do some damage.
I now have to pay £160 to get the locks changed, and I have to report it to the building owners to get the front door of the apartment building locks changed and I'll have to pay for everyone in the building to have their keys changed for the main door.
can I press charges for this, is it classed as theft?


I'm not in the UK but I don't see this as theft. I do see this as a small claims suit for the money you have to spend.

Did she leave anything? Did you specifically inform you that she had vacated?

But yes, there is no criminal action here, but you certainly can file a civil action to recover your costs.