Angus Crawford is a news correspondent for the British Broadcasting Corporation.

The inquest into the death of teenager Molly Russell is due to start next week.
Molly, who was 14 at the time, took her own life after viewing material about suicide and depression on social media.
Ian hopes it is a turning point.
"I hope that we will learn lessons and that it will help produce the change that's needed to keep people safe," he said.
Mr Russell thinks long-term exposure to harmful material was a factor in Molly's death.
New legislation was inspired by Molly's story. The online safety bill is still going through parliament and will get a third reading in the Commons.
The inquest into the death of a person is due to last two weeks. The executives were ordered to appear in person by the coroner.
A number of internal documents have been revealed by the former employee and whistle blower. The impact of the platform on the mental health of young people was researched by the company.
In the last six months of her life, Molly liked more than 11,000 pieces of content on her social media accounts. She is thought to have used the image sharing site more than 15,000 times.
Andrew Walker has been warned that some of the content is difficult for adults to look at for a long period of time.
Mr Russell's campaign to prevent future deaths was a hugely significant contribution to the agenda of suicide prevention in this country, according to Ged Flynn, chief executive of Papyrus.
He said that they had to change the way they accepted the power of the tech giants.

The inquest may be a "watershed moment" according to others. Molly's death is a tragedy that is all too common to all parents who worry about the risks their children face online.
Big tech representatives will be questioned under oath about how their products may have contributed to the death of a child.
Meta will continue to assist the coroner in the Molly's family inquest. We don't allow content that glorifies suicide or self-destructive behavior.
"Combating self- harm is a priority for us as we strive to ensure thatPinterest plays a positive role in people's lives," the company said.
Matthew Bergman is a lawyer from the Social Media Victims Law Centre in the US.
Regardless of the outcome, the fact that Meta senior personnel have to testify is a step towards accountability.