I know we only tend to hear about poor experiences as happy passengers don't post so often but this does not reflect well for P&O.
Passengers’ Christmas Day ‘ruined’ on P&O cruise | News | The Times
The delay is measured by CAA as time between scheduled arrival time and the time first passenger being able to get of plane. Airlines may try and fob you off that arrival means touchdown, it not it's when first passenger is able to get off.
3 72hr delay gets you statutory compensation.