By Fergus Walsh
BBC News Medical Correspondent
The disease has spread west from Asia
Month by month, mile by mile, migrating wildfowl have spread bird flu from south-east Asia across Europe.
It was inevitable the disease it would end up here. The UK is now one of 13 EU countries to have the infection in wild birds.
At the moment, the danger is almost entirely to birds. It is lethal to chickens.
Ducks, geese and other wildfowl do not always fall ill and can spread the virus - hence the danger from migrating birds.
That's why it is crucial domestic poultry are kept away from wild birds. To date there have been very few infections in poultry flocks in continental Europe.
In the UK risks to humans are non-existent unless you touch an infected bird. Nearly 200 people around the world have caught bird flu - about half died.
A crisis of consumer confidence is currently the biggest threat the UK is facing
The virus is contained in bird faeces and bodily fluids.
In rare cases these can be breathed in or ingested - lodging in the lungs and then mounting a violent attack on the respiratory system.
The big fear is the H5N1 virus will mutate to be infectious between humans.
One way it could do this is if it infects someone who already has normal flu.
The two viruses could mix and a new pandemic strain of flu could result with the ability to pass between humans.
But there is no sign this is about to happen. It may not do so for many years.
That is why Britain is building up a stockpile of Tamiflu - an anti-viral drug which can prevent the virus from taking hold in the body.
And in the next few months the first doses of a prototype vaccine against H5N1 will arrive in the UK. Enough to immunise well over a million key workers. This would be done only if a pandemic threat is imminent and there's no guarantee it will work.
It's crucial that you stay away from any sick or dead wildfowl.
And although cats have recently been infected with bird flu in Germany, there is no need to bring pets indoors unless you are near an infected area.
There is no reason why people should stop eating chickens or turkey. There is zero risk from meat and eggs as long as they are cooked.
And, of course, with no bird flu in our poultry flocks - a crisis of consumer confidence is currently the biggest threat the UK is facing.