job offer-are there any take-backs?


Hi all,
So got a job offer over the telephone yesterday, and they said they would be sending me a official offer letter by post.
I was just wondering if there is any chance that they may be decide to take back the job offer.
I still have to provide 2 references and sign contracts etc, so I wasn’t sure how “solid” the offer is.
I do have a couple of interviews in about a week and a half, and would like to give those companies sufficient notice that I won’t be able to make it so that they can inform other people waiting that slots for interviews have opened up. But I also don’t want to lose those opportunities without confirmation from this one.
Any help would be very much appreciated.