Lord Blair led the force for three years between 2005 and 2008 and was in charge during the 7/7 London bombings.
This breaking news story is being updated and more details will be published shortly.
Please refresh the page for the latest version.
You can receive breaking news alerts on a smartphone or tablet via the Sky News app. You can also follow us on WhatsApp and subscribe to our YouTube channel to keep up with the latest news.
