A 21-year-old man has been arrested at Gatwick Airport on suspicion of training for terrorism overseas, police said.
The man had returned to Britain on a flight from Istanbul and remains in custody at a west London police station, a statement added.
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In an audio statement given by the remaining Japanese captive, IS said they would let him go in exchange for their 'imprisoned sister'.
It will be a little warmer than yesterday for most, but the day will largely be punctuated by cloud and scattered showers.