Firstly the staff are asked to use the cheapest methods possible. This includes deciding if they can travel up and down in a day and fore go the cost of an overnight stay and the expense of food claims too!
Many govt departments don't allow domestic flights for environmental reasons. I'd be surprised if they are permitted in the Treasury which I understand is driving the carbon zero message across government. Doubt whether flights will beat the train for convenience. I'd also imagine that as belts tighten, travel budgets will be the first to be looked at after people have spent a year working on Teams.
Other points are spot on - no downside to having those jobs local.
Not aware of the point N707ZS is making, but presumably he means that not all the areas of the freeport will get the tax reductions on new buildings and other investments? If so, the other areas of the freeport will jump to the front of the new investment queue ahead of the airport