Abandoned turtle/tortoise

[loodoo100]

Hi, I've already posted elsewhere but my query now is as follows. My friend recently moved into a flat and found what she thought was a tortoise in the garden. She immediately thought it had been abandoned by the previous owners of the flat who were not nice people. I'm now looking after it and I posted a photo of it on this forum. A few people thought that it might be a turtle. Can someone please advise. Thanks in advance.