I hope I can explain this....
We have paid off our mortgage in full and our house is worth £150k.. We have £50k in savings.
We have found a house we want to move on which is on the market for £250k. Ideally we will sell our house and take out a 50k mortgage to buy the new house.
We can actually get a mortgage for the full property price (with our savings as a deposit) If we can't sell our house quickly, would it be worth doing this and becoming first time buyers? So we don't have to sell our house and thus break the chain and proceed. If we can a mortgage with no early redemption fee, we could then pay the mortgage mostly off when we sell our house.
Does that make sense? Is it possible?