There appears to be two questions:
Can someone please explain the regulation about temporary non-residence in the UK, in reference to someone returning to the UK after a period abroad.
See my first posting above.
Are there any other regulations which define the tax liability of a lifelong UK resident who moves overseas indefinitely
Once you have left the UK indefinitelty you are outside the scope of UK income tax (except re UK source income) and outside the scope of UK CGT; you may even acquire a non-UK domicile.