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Hi guys, sorry I haven't replied earlier.
I checked with the police and they said as long as it belongs to you, you can do what you want.
So, I thought I'll check with the land registry first to make sure it is actually mine.
Turns out that particular garage does not belong to me, but the one next to it is mine. (The reason I thought the first one was mine was that was the one the estate agent showed me and that was the one the previous owner said belonged to the house.)
The guy in the flat upstairs is using my new garage and I think his landlord is using the old one. I have showed him the documents and he has agreed to move his stuff out ( he is moving out the flat anyway).
To get the stuff out of my first garage, I am going to push a note under to ask him/her when I can get my stuff out.
I bought my flat 9 months ago and all I have had is problem after problem!! Wish I just stayed renting!