Airlines have threatened to take legal action against Heathrow if a settlement is not reached over the costs caused by the airport being shut on Friday. The chief executive of Heathrow Airline Operators' Committee Nigel Wicking - which represents over 90 airlines using the airport - said he hoped the matter could be 'amicably settled at some point in time'. He told Sky News :'If we don't get good enough recourse and repayment in terms of the costs, then yes, there might be a case for legal action. 'I would hope not. But in some of these situations that's the only course once you've gone through everything else.' Mr Wicking also wants an independent investigation of what went wrong and why it took so long for the airport to get back up and running again. Experts say that airlines and suppliers alone could face costs of 'at least' £20m for the day of disruption. This figure includes an estimate of expenses for passengers, crew accommodation, additional transport, fuel and other costs for the aircraft themselves. Nearly 300,000 passengers were affected by the meltdown, which led to the cancellation or delay of more than 1,350 flights. Ed Miliband ordered an urgent investigation into the Heathrow fire after the airport boss claimed he is 'proud' of how the power outage was handled. He is working with Ofgem and using powers under the Energy Act to formally launch the grid operator's investigation. 'We are determined to properly understand what happened and what lessons need to be learned,' Mr Miliband said. 'That is why, working with Ofgem, I have today commissioned the National Energy System Operator to carry out an investigation into this specific incident and to understand any wider lessons to be learned on energy resilience for critical national infrastructure, both now and in the future. 'The Government is determined to do everything it can to prevent a repeat of what happened at Heathrow.' Earlier, the airport's chief executive Thomas Woldbye was grilled over claims that Europe's biggest airport had become an international 'laughing stock' after a substation fire caused a temporary power loss and forced hundreds of flights to be grounded on Friday. But despite the ongoing chaos, Mr Woldbye told BBC Radio 4's Today programme he was 'personally quite proud' of his staff's response to the unprecedented scenes and appeared to shift the blame for the outage. 'Don't forget the situation was not created at Heathrow Airport. It was created outside the airport and we had to deal with the consequences,' he told presenter Emma Barnett on Saturday. The airport boss, whose salary is believed to be around £5million a year, also refused to comment on whether he should still be in his role following the disaster, saying 'I will let others judge if they think there is an issue'. It emerged over the weekend that Woldbye went back to bed to make sure he was 'well rested' rather than work through the night as the fire raged through the power substation. He was at an event in central London when the power first went out at 11pm on Thursday, prompting him to return to the airport west of the capital. When the scale of the incident became clear, senior leaders were split into two 'gold commands'. In the early hours of Friday, it was decided that Woldbye's command group would go to bed. His deputy Javier Echave was left in charge and he took the final decision to close the airport, sending a notice to air crew at 1.44am. Woldbye resumed work by phone at 7.30am and was in his office at Compass House, Heathrow's head office, shortly after 9am. Insiders told the Sunday Times that the decision for Woldbye to go to bed was taken on safety grounds. It was felt vital that the person at the top was well-rested to make clear decisions.Sean Doyle, chief executive of British Airways, and Shai Weiss, the Virgin Atlantic boss, were reported to have worked through the night from their headquarters. A Heathrow spokesperson told MailOnline: 'We do not recognise the description of proceedings as set out in the Sunday Times. 'We have a robust crisis protocol that ensures we have experienced leaders able to take key decisions having had adequate rest - without compromising passenger or colleague safety by being too tired. 'This protocol was followed so that Thomas, and his whole senior leadership team, were exactly where they were supposed to be during an incident of this scale. Under round-the-clock leadership, teams across Heathrow were able to fully reopen in 24 hours and deliver an extended schedule on Saturday. 'While we are sorry that passengers and customers were impacted by the closure of the airport on Friday, our performance in safely accommodating over 250,000 passengers on Saturday shows that the correct decisions were taken at the right time. 'While some commentators spread ill-informed misinformation, we will focus on serving our passengers.' The National Energy System Operator (Neso) is expected to report to the Department for Energy Security and Net Zero and Ofgem with initial findings within six weeks. Operations at Heathrow were normal on Saturday morning after flights began taking off on Friday following hours of closure after a blaze at an electricity substation in Hayes cut power to the west London airport. The unprecedented shutdown of Britain's busiest airport grounded flights for most of the day and exposed a major vulnerability in the country's infrastructure. A probe into the disaster was being led by counter-terrorism police, while Westminster sources blamed human error. Some 120 transatlantic services were forced to turn round in mid-journey. Passengers on flights from Singapore and Perth were diverted to Paris before taking buses to London. As eight long-haul British Airways flights finally took off on Friday night, analysts criticised the airport, the busiest in Europe, for its inability to rely on backup power. But Heathrow bosses are facing questions about how a small fire shut down one of the world's biggest airports. Phil Hewitt, director of energy analysis firm Montel Group, said: 'This potential lack of resilience at a critical national and international infrastructure site is worrying. Heathrow has its own biomass power plant and diesel backup generators, but they can power only essential safety systems, such as lighting and exit doors. The airport's electricity usually comes from three substations, each of which has a backup transformer. In the case of the damaged North Hyde substation, in west London, its backup transformer was also lost in the fire, which started shortly before midnight on Thursday. Within hours, theories were swirling that sabotage, possibly even by Russia, may have been the cause. Despite the involvement of counter-terror officers, Scotland Yard said it was 'not treating this incident as suspicious, although enquiries do remain ongoing'. 'Various specialist investigators continue to examine the scene and it is expected to take some time before full assessments can be completed,' a spokesman said. A Heathrow spokesperson said: 'This was an unprecedented issue which began with a fire at an off-airport substation, in less than 24 hours the entire airport was rebooted from a standing start and we delivered a full schedule from Saturday onwards. 'There are two reviews into the systems and response both at Heathrow and with the wider grid infrastructure. We will support these and lessons will be learned where needed. 'Every penny we invest in our airport infrastructure is approved by airlines and our regulator. On a project-by-project basis, they oversee and influence how we build and maintain Heathrow.