As it stands at the moment, there is an imbalance at Level 5. Assuming that Hickley are promoted from Nat3Mids in place of Ampthill, Nat3 North has 15 clubs, Nat3 London has 13. So, a club will need to LT from North to Midlands, which in turn will push a club from Midlands to London (for the latter, I am assuming this will be easier than a double transfer: Midlands->SW and SW->London).
It is entirely possible that Stockport will replace Ampthill in National 2 (rather than Hinckley, in which case there will be 15 Clubs in Nat3Mids and 13 in Nat3London.
So, first question: who is likely to move from North to Midlands? A Cheshire club? Stockport? Chester are exempt - there is a 2 year grace period on a club that gets Level Transfered back to where they belong. Chester returned to Nat3 North at the start of this season (from Nat3 Midlands) so have another year of Nat3 North, unless they volunteer. Or a South Yorkshire club? Sheffield Tigers, perhaps?
Secondly, who is likely to move from Nat3 Midlands to Nat3 London? An East Midlands Club, I would think. Again, Luton are exempt. Ampthill? Newly promoted Old Northamptonians? Peterborough even - close to places like Diss and North Walsham.