Thank you for all your responses, my son in laws account has had the 'pending' amount drop off but he has still sent a complaint email to p&o as several of his direct debits were returned because of this with the resultant charges and a detrimental effect to his credit score!
As P&O seem to be moving towards a younger demographic of passengers surely they need to realise that many young couples do not have surplus cash to cover these pending transactions... my son in law and my daughter had budgeted carefully for their trip and stayed within their means, however with p&o putting a 'hold' of more than double their spending on their bank account they were left in a dire situation.
They may be in the 0.1% that p&o choose to ignore at the moment but as more and more younger people try cruising that percentage will grow and will not be able to be ignored if p&o want to maintain its share of the cruise market.
Once again thank you for all your advice and comments.
Happy cruising everyone.