We still have a bit of time before our application, but are trying to understand how the system works.
We might move to another area of London (from Southwark council to Wandsorth), mainly because of better transport links (schools are good where we live and seem less oversubscribed). One of the many options we are considering (among moving to some tropical island and opening our own bar!) is to hold on to our current property, renting it out for about a year, then selling it. We need to sell within 18 months of buying elsewhere, otherwise we don't get the additional 3% stamp duty back. Not entirely sure it makes financial sense (we still have to run some numbers) but that's not the question.