Before I moved I tried to find a flat and found that letting agents had no interest in helping from the US. At all. So, I found someone looking for a roommate. I forget the site...it was like easyroommate.co.uk or something like that. We had a hotel booked for when we first arrived, then I met the guy, we agreed about the room and I moved in a few days later. This gave me a place to stay while I looked for something more permanent. I lived with him for just over a month then I found a flat on rightmove.co.uk.
I know it's not ideal as a couple to move into a shared house, but it does give you time to get your feet on the ground, a chance to explore your town to determine where you would want to rent a flat, and an address so you can get a bank account which makes getting a lease a lot easier. It's also easier to find people willing to do short term in a shared house than someone willing to do a short term flat rental.