On 17 October 2023 a Boeing 737-800 passing FL130 after departing Manchester received a cabin pressurisation warning and the crew recognised that both engine air bleeds were off. After correcting this, climb was continued without donning oxygen masks until a related air conditioning pack fault occurred which prompted the operator to request a return which was uneventful. The bleed-off condition had arisen after maintenance and had then not been recognised at release to service or during crew pre and post flight checks. The non-compliant crew response to the subsequent situation was found to have been both deliberate and unjustifiable.