Trade union activists at the traditional May Day march across the capital used this year's event to pay tribute to late RMT union leader Bob Crow and Labour MP Tony Benn.
TUC General Secretary Frances O'Grady said they would both be 'hugely missed'.
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The notices have been posted in Covent Garden are thought to be aimed at organised criminal gangs.
A cloudy start to the short Christmas week. It's gong to be a mild one though with temperatures already above the double figure mark.
As we move into a shorter working week for most people, we are looking at a generally cloudy one.