At the moment I live alone in a three bedroomed house worth approx £200
I would like to rent this out and buy a smaller house paying the mortgage off with the rent from my main house. Do you think I am likely to get a mortgage on predicted rent income?
You mean take out a buy-to-let mortgage on the existing property of, say, £120k and use the proceeds to buy a smaller house for yourself outright?
BtL mortgage companies might agree to that as a proposition, provided you are stumping up (say) £80k of equity.