Would Ukip win a battle for Portsmouth South?

Downing Street aides nervously run through the symptoms: a flat economy, poor press, leadership mutterings. Then they say, ‘It’s just mid-term blues, isn’t it?’ A second later, they add nervously, ‘It’s nothing more serious than that, is it?’ The truth is, nobody can be certain. There’s no reliable way of distinguishing mid-term blues from something politically fatal.