Boris Johnson has insisted he won't allow a third runway to be built at Heathrow Airport, amid speculation that senior Tories want to revisit the idea.
The Conservative Mayor of London, fighting for re-election in May, says the move would be "intolerable" for people in the west of the capital.
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Specialist explosive detection dogs searched through the town examining letter boxes and phone booths for signs of potential devices.
Temperatures soared to 27.9C in Northolt shortly after midday on Thursday, making it the warmest April day for 69 years.
The South East will enjoy the best of the weather and along with Paris will be the hottest place in Europe.