Sorry just re-reading the above, do they rescreen the passengers before the diverted flight departs again ??? That’s beyond stupid surely.
Yes, that's another example of silly DfT rulings (Nothing to do with European rules). However, the requirement can be waived under certain circumstances. An Aer Lingus diverted into MAN a few weeks ago and EI operations had to prove to the MAN Duty manager that all the pax were unaware that the aircraft would divert to MAN at the start of their journey. All pax were allowed to stay on board.