In 2018 Xiaomi opened an official store in the UK, and now they closed it. Together with the store the Twitter account and the Mi Store page on the Westfiled website are gone too.
This closure is not because of the Coronavirus outbreak. You can still buy Xiaomi products from their website, also from Amazon.
In an official statement to Android Authority, Xiaomi said:
“This adjustment to our local retail strategy is a reaction to our fast-growing business in Western Europe. Since our official arrival in the UK over one year ago, we have loved building relationships with our users, Mi Fans and partners and thank them all for their support. UK users and Mi Fans can continue to purchase Xiaomi products through our official website mi.com/uk and other official channels that will be announced along with our product launches in the future.”