The Rail Maritime and Transport Union said that it was balloting drivers on the Picadilly line in a row over working conditions and agreements.
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Fighting for their right to misuse nitrous oxide, approximately 60 or 70 protesters inhaled 'laughing gas' amid concerns over a clampdown.
The pilot, from the Gnat private display team died after the display aircraft he was in crashed near the CarFest event in Cheshire.
The annual cycling festival in London was the biggest ever this year - with more than 25,000 taking part today.