In the film two aircraft collide above London
The Day Britain Stopped is a drama filmed in the style of a documentary set in the future and is, therefore, quite different to traditional news and current affairs programming.
But why mix fact with fiction at all?
"We work within a safety margin in the UK - but we are heading towards maximum capacity and with that comes less of a margin. If something goes wrong, and it does not have to be major, the consequences can be incredibly damaging and far-reaching."
Professor Phil Goodwin,
Government Transport Adviser 1997-98
Last year, the BBC broadcast a drama that explored the consequences of a bio-terrorist attack. The programme was made in the style of a documentary, and looked at a fictional smallpox outbreak.
All the events in the fictional narrative, aside from character development, are based firmly in fact
It was clearly set in the future but by appearing so authentic it ruffled feathers. But it also fulfilled a journalistic objective of exploring the hypothetical consequences of a real threat in a realistic way.
Drama filmed in the style of a documentary itself may not be a new format, but using actors to give hindsight interviews and illustrating them with mock archive footage proved a powerful vehicle and brought a new audience to current-affairs.
The BBC asked production TV company Wall-to-Wall to explore other scenarios which would also raise issues worthy of national debate.
But what subject matter could compare with a global pandemic that wiped out 60 million lives - and not appear as scare-mongering?
Finding a focus:
The development team turned away from apocalyptic thoughts and towards something that on the surface might appear almost mundane - transport.
Everyone agreed that our transport networks are crumbling from decades of under-investment
The government's transport policy was seen by many as being in disarray, with John Prescott's 10-year plan under review and Britain plagued by the most congested roads, the worst commuting times, and some of the highest public transport fares in Europe.
The production team approached a wide range of academic and government experts, the emergency services, transport unions and consultancies, to see if there was any consensus about the nature of the country's transport crisis.
Many of them welcomed the unusual opportunity that a confidential briefing gave them to vent their frustration at a deepening crisis.
Snow brought gridlock to the roads in January 2003
Almost everyone agreed that our transport networks are crumbling from decades of under-investment, we needed a specific focus.
But it became clear that the issue of capacity should be our overriding concern.
By opting for a chain-reaction narrative, we tried to underline the fact that our national transport system runs on a knife-edge.
It may function efficiently for much of the time, but each network handles such volumes of traffic that when something goes wrong, it can result in chaos.
The most vivid way to illustrate our concerns was to dramatise them.
The film is intended to test Britain's transport infrastructure to destruction, but as a journalistic exercise designed to expose the way we run our roads, railways and air traffic systems.
All the events in the fictional narrative, aside from character development, are based firmly in fact.
But since it is about a possible future, the most vivid way to illustrate our concerns about how little it would take to paralyse Britain's entire transport system, was to dramatise them.
We dramatise an unprecedented gridlock situation, prompted by sheer weight of traffic, poor weather and accidents at key points on the roads.
The aviation industry will close ranks and cast doubt on the credibility of this
In our film tens of thousands of motorists are trapped overnight in freezing conditions, and a handful die from hypothermia.
The events at the end of January when two inches of snow, high traffic volumes and accidents turned the M11, A14 and other roads into car-parks overnight, showed that our scenario was not fantastical.
Undoubtedly, the most controversial element of The Day Britain Stopped will be the mid-air collision over London. Much of the aviation industry will close ranks and cast doubt on the credibility of this.
Lack of runway capacity puts pressure on controllers
But our research revealed that those contracted to advise the national air traffic management (Nats) on safety have identified shortcomings in a specific procedure in operation at Heathrow - missed approaches.
We also believe from a series of confidential briefings (it is a disciplinary offence for Nats employees to speak to journalists without prior notification to their superiors) that the pressures on air traffic controllers are growing, principally due to the lack of runway capacity within the present system.
Experts will point to statistics that indicate the remarkable safety record of commercial flying, and we're not suggesting that people should be dissuaded from taking to the skies.
In truth there is not a policy of zero-tolerance when it comes to air safety
But nor do we believe that our national air traffic management should trade on its past reputation, or obstruct legitimate journalistic inquiry.
Loath as our air traffic management authorities are to admit it publicly, in truth there is not a policy of zero-tolerance when it comes to air safety.
The Day Britain Stopped is undoubtedly a frightening film. But it raises serious question about the potentially catastrophic consequences of our crumbling transport infrastructure.
We all regularly encounter traffic jams and flight and train delays. But these are merely symptoms of a capacity crisis that is placing more pressure daily on those entrusted with keeping our transport systems moving safely - or moving at all.
The Day Britain Stopped was broadcast on Tuesday, 13 May, 2003 on BBC Two at 2100 BST.