@Timmy2wheels and @chrisbmx116 - many thanks for the feedback. Genuinely appreciated.
As we will be on the other side of the planet, we are resigned to having to use a managing agent. Collection of rent, management of taxes and the mundane issues that may arise are better handled without a twelve hour time difference.
The agents that we are speaking to at the moment seem to want T's crossed and i's dotted so unlikely that they would take on our flat without the lender giving explicit agreement.
The mortgage guy is a friend and has been pretty good with free advice to date so will part with the cash in this instance. Also, the clock is ticking as we are looking to be out by Christmas.
This move is, however, presenting new costs every day. Sigh.