Will Rochester and Strood come to be seen as the turning of the tide for UKIP? The turn of a tide is always difficult to spot at the time. Waves come and go, but eventually the direction becomes clear.
The peak support in a national opinion poll for UKIP so far is 25% in the Survation poll on 10 October 2014. Survation tend to show the highest figures for UKIP support among the polling companies, but their more recent polls have shown UKIP support below the peak at 23%. Populus tend to show the lowest levels of UKIP support. Their peak figure was 15% and their most recent poll showed 11% support for UKIP. The recent trend in UKIP support from all the major polling companies is down, not up.
The peak of 25% UKIP support compares to the peak for the Liberal Democrats of 34% before the 2010 election and 50.5% for the SDP/Liberal Alliance in 1981.
The scale of defections to UKIP is still much smaller than those to the SDP in the 1980s. The SDP received 28 sitting Labour MPs and one Conservative.
The history of new parties is one of fragility. The British Union of Fascists, the SDP, the New Party, Veritas, Common Wealth and the Referendum Party all came and went. UKIP has shown a tendency to fragment. Of the 13 UKIP MEPs elected in 2009, five (38%) had left the party by the time of the 2014 European election.
Overall, by-election victors who capture a seat from another party have on average around a 50% rate of retaining the seat at the following general election. The opinion poll from Lord Ashcroft completed on 10 November showed UKIP on course to win the Rochester and Strood by-election on 20 November, but likely to lose the seat at the general election in May 2015.
It is not easy to spot the change in a tide. But tides do tend to turn at some point.