Mae’r sefyllfa waethaf resymol a gyhoeddir gan Lywodraeth Cymru yn tynnu sylw at y ffaith y gallai 40-70% o’r Cerbydau Nwyddau Trwm sy’n cyrraedd y porthladdoedd wedi diwedd y Cyfnod Pontio gael eu gwrthod gan nad oes ganddynt y dogfennau iawn.  Mae disgwyl i’r uchafswm fod yng nghanol Ionawr, ond mae angen gwneud trefniadau erbyn diwedd y cyfnod Pontio o hanner nos ar y 1af Ionawr.
The reasonable worst case scenario published by the UK Government highlights that 40-70% of HGVs arriving at ports after the end of the Transition Period could be turned away as they do not have the right documentation.  The peak is expected in mid-January but the plans need to be in place by the end of the Transition period on midnight 1 January.