The best comparisons are the Uxbridge and Beckenham by-elections in 1997 when the Tories were even further behind Labour than Labour are behind the Tories now. In Uxbridge, despite their dreadful poll ratings, the Tories got a decent sized swing towards them in Beckenham there was a moderate swing to Labour. If there is a swing to the Tories it is absolutely awful showing, if Labour manage to lose it then they have managed to do worse than the Tories at their nadir when they had only 165 MPs...
Uxbridge was due to the death of the sitting MP; Beckenham was the result of a scandal where the sitting MP had left his wife for his secretary, or something like that.
