The Liberal Democrat leader Nick Clegg has admitted his party will face a tough fight in London at the next election, when Brent Central MP Sarah Teather stands down.
Last week the former education minister criticsed her own party and announced she was quitting in 2015. In an interview with ITV News, Nick Clegg said he knows the keeping the seat won't be easy. He spoke to Paul Brand.
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Paramedics were on standby outside the police cordon as armed officers stood by the property.
A team of researchers has taken samples from the ten busiest London Underground lines to work out which are the dirtiest.
The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.