Political questions remain over cargo bombs
Questions are being asked in London about why the prime minister was only told of the cargo bomb threat some 10 hours after the US president.
The intelligence tip-off from Saudi Arabia arrived in Washington early on Thursday evening.
President Obama was first informed of intelligence about a threat by his assistant for homeland security and counter-terrorism, John Brennan, at 2235 Eastern Time (0335 BST), with e-mails continuing through the night. Mr Brennan also began meeting and talking to other US officials.
But in the UK, Prime Minister David Cameron was apparently not informed until mid-afternoon on Friday when it was confirmed that a device had been found.
The exact wording of the original intelligence is unknown but probably talked of parcels heading for the US. Officials in London have always said they do not believe the UK was a target and it was essentially chance that the package passed through the country en route.
Thanks to the intelligence tip-off, the police in Britain identified a suspect package on board a UPS courier aircraft which had landed at East Midlands Airport en route from Cologne to Chicago in the early hours of Friday morning.
However, they failed to find the explosives in an initial search. It was only after re-checking the intelligence that there were further searches and the explosives concealed in the printer were found.
As this process was unfolding Mr Brennan held phone calls from Washington with a deputy national security adviser in Downing Street at 1015 and 1215 London time, to receive updates on the packages.
Some officials in Britain were still unconvinced at this point that there was any real threat. In Britain, the transport secretary had been informed initially in the morning, because of the closure of the airport. The home secretary was told later, when it was clear the package really was suspicious.
It was only as more forensic tests were carried out that the certainty increased, in London, that the devices were real bombs and not just a dry run or a hoax.
In mid-afternoon, a meeting of the Cabinet Office's emergency committee COBRA was called to discuss events. President Obama was briefed in the Oval Office around the same time by his officials.
Mr Cameron is reported to be unhappy that he was informed late in the afternoon. Part of the reason could have been that he was away in Brussels for a European summit and only returned on Friday afternoon, but this would not have prevented a phone call being made.
It also reflects different roles American and British political leaders have tended to play. The issue of "who knew what when" has become increasingly political in the US.
In the wake of the Christmas Day failed bomb attempt, there was criticism over whether the US national security machinery had worked properly and whether the president had spoken about events quickly enough.
There may well have been a desire not to be seen to have been caught flat-footed again, especially with US mid-terms only a few days away.
The culture in Britain has tended to be different and in this case officials appear to have been more cautious about the seriousness of the plot.
But even though standard protocols may have been followed, the decision not to directly inform the prime minister by officials in Downing Street, as the investigation unfolded, still appears surprising and is unlikely to happen again.
The case has raised wider questions about when and under what circumstances you should wake up a leader.
Tony Blair's former chief of staff, Jonathan Powell, said prime ministers and presidents should only be woken up if there is a decision to be made.
"Why on earth wake up David Cameron and send him off to East Midlands airport to start rooting through the boxes of UPS mail looking for a bomb? It's ridiculous," he told the BBC.
"Personally having seen leaders close to, I'd much rather they slept, they make much more rational decisions if they sleep the night. They get little enough sleep as it is, so I'm for letting sleeping politicians lie."