Hi,
I can't exactly speak to the UK/US situation, but my experience might be of help to you. I owned a house in Denver when I got a job in Savannah. My plan had been to sell after I got settled down there but 2008 had other plans for me. Needless to say, I couldn't sell, so I rented. But, I had an ARM and a second with an insane interest rate, because I had to do so many repairs when I bought the place. To try to get control over my financial life, I tried to refinance, and I couldn't. Even though I was only renting in Savannah, they considered my house a "second home" which I didn't have the income to support. When I said I had renters in it, they told me income property is refinanced differently, and I needed to show 3 years of solid income from the property on my taxes. Long story short, my renters trashed the place and skipped town. I actually wound up quitting my job and moving back to Denver because of it, although it was no great loss, as I wasn't really happy in Savannah in the first place. I was able to refinance once I got back and settled in the house, and now have a great rate that will never change. Still, I could have refinanced if I had a record of income from the property.
This time, I am turning the rental over to a property manager, and will be getting enough to cover all the bills and be able to put some aside for repairs. Now I just need to figure out how to do my taxes with all this...
I hope that helped in some way. Good luck though, and I hope you can do the refi. One note, if you have or could have USAA, because they deal with service members and foreign postings, they actually have a lot of stuff they can do banking-wise on an international level. I can actually get a car loan for a UK vehicle as soon as I arrive. They will even help me with the actual purchase.