Even with very good UK credit and both of us being citizens (I'd gained BC about 6 years earlier) we were asked for 6 months rent in advance at the last place husband and I rented. Reason, I was in full-time employment but husband was self-employed. My salary wasn't enough to alone so they asked for 6 months rent in advance.
It sucks, be prepared for 6 months rent in advance, or people to not want to rent to you, depending on your financial situation.