£180 million worth of train carriages built at Derby-based Bombardier will be on show for the Transport Minister, Patrick McLoughlin, today.
The 130 carriages are being tested in London and will be rolled out across the city in December.
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Fog patches and extensive low cloud at first will steadily lift and clear.
A murky start with mist and fog then gradually clearing, although some eastern coastal districts may remain cloudier.
Isolated showers should die out through the evening to leave a dry remainder of the night.