Boris Johnson said today he could not go on "endlessly dodging" questions about his future.
But the Mayor of London played down his chances of success, saying it was "highly likely" he would fail to find a suitable constituency in which to run.
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Temperatures will reach around 28 Celsius (82F) at their highest.
A minute's silence will be observed at 11am on Thursday in remembrance of those who lost their lives in the Manchester Arena attack.
New research has found those who consumed two cups had a 35% reduced risk, and for those who drank five cups, the risk halved.