Headcounts
Two systems operate here the ticket coupon reconciliation i.e. the number of coupons checked in at the gate should amount to the same number as the headcount perfomed by crew or groundstaff. However, I have witnessed different totals on aircraft with only 29 seats so what hope with 400 plus.
Prior to departure of a transit flight a print out of the seats occupied by transiting passengers is generated for the aircraft dispatcher / co-ordinator to confirm and sign legal documentation to the accuracy of the figure and for a futher count of the total (including joining pax) on the departing flight.
UK aviation law makes it a criminal offence for a UK registered plane to depart without an accurate reconciliation from within the UK and also whan a UK registered a/c departs outside the UK.
This applies to aircraft over 15 tonnes only.