Slide bush? (HP13 near railway station)

This was sold to me as a patio plum tree but I believe it's a sloe berry as the fruit looks like plums but the size of sloes
 I've just dug it out of the ground and it's currently looking very healthy but would need to go back into the ground or a pot ASAP..
Let me know what time and what day you can collect it.

Fair Chance Policy: I’ll wait before choosing a recipient to give more people a chance to reply.