A pilot tasked with flying a 'Moyes out' banner over Old Trafford says his company received the call two days ago - shortly after United went down 3-0 at him to rivals Manchester City.
Air Ads' chief pilot Chris Mustow also told ITV News' Ian Payne that, while the company had to be wary of public order issues, he was confident "we're not going to cause a riot".
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Among those murdered was Keith Palmer, an unarmed constable who "did his job and never wanted any fuss."
Top temperature 14 Celsius (57 F).