St Petersburg marked earth hour by turning out the lights of Palace Square. Climate change protesters held a candle lit vigil at 8.30pm local time.
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Most parts of the country will experience near unbroken sunshine after a chilly start to the day.
As the investigation into Khalid Masood continues, former acquaintances tell of violent incidents in the murderer's past.
Local authorities say the current system of Traffic Regulation Orders are time-consuming, expensive and bureaucratic.