Snow is because of fall in London from round noon, whereas the Met Workplace says it should really feel like -3C.
Source : https://www.standard.co.uk/news/london/met-office-yellow-warning-snow-london-b1130770.html
London weather: Snow falls in capital as Met Office issues new ice warning - London weather: Snow falls in capital as Met Office issues new ice warning * London weather: Snow falls in capital as Met Office issues new ice warning | London weather: Snow falls in capital as Met Office issues new ice warning | London weather: Snow falls in capital as Met Office issues new ice warning | London weather: Snow falls in capital as Met Office issues new ice warning | | London weather: Snow falls in capital as Met Office issues new ice warning | | London weather: Snow falls in capital as Met Office issues new ice warning | London weather: Snow falls in capital as Met Office issues new ice warning