I withdrew back in February.
I didn't have to tell student finance as the uni seemed to sort it all out for me. Other unis may be different though so I'd check just in case.
I also had to pay back £1300 of the maintenance loan for the year (which had to come out of my savings as I'd already spent it on accommodation. Ouch). Wasn't the nicest letter to get through the post.
Worth it though as I'm now about to start a more suitable course at a different uni next month.