Unite joined the protest in London against the closure of the company which makes black cabs.
Unite's Peter Rose said: "We're here today because we want to campaign to keep the black cab built in Britain. It's been here for over 70 years and we want that to continue. It's a London icon, deserves its place in London."
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The 47-year-old man died shortly after 3pm on Tuesday.
Specialist explosive detection dogs searched through the town examining letter boxes and phone booths for signs of potential devices.
Temperatures reached 29.1C in St James's Park, central London.