The motorcyclist is said to be aged in his early 20s and was wearing light grey tracksuit bottoms with a double light blue stripe down each leg, a black jacket and black gloves which had plastic caps on the knuckles. He was also wearing a green and silver crash helmet.
The bike he was riding is described as a black and green off-road machine with Evo-Tech written on the front shocks.
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Monday's lunchtime weather for the West of the region
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The long-awaited recommendation on whether Heathrow or Gatwick should get a new runway will be made on Wednesday.