AC Milan director Umberto Gandini has tweeted:
Very proud of the Milan players who decided to walk off the pitch today for racist abuse from few idiots! No racism, no stupidity!
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Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.