Shaun Woodward will step down as the Labour MP for St Helens South ahead of the next general election in 2015.
Woodward has been an MP in the town since 2001.
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More than £1.5 million has been raised in the wake of the terrorist attack in Manchester on Monday night.
Chelsea football club has cancelled a homecoming parade to celebrate their Premier League title win.
Twenty-two people, including children as young as eight, were killed and at least 59 injured during the suicide attack.