Ukip may never have won a seat in the House of Commons, but today it has overtaken the Liberal Democrats as the third most popular party, if a YouGov poll for the Sun is to be believed.

The daily poll puts Nigel Farage’s party on nine per cent, one point ahead of the Lib Dems, who have eight per cent of the vote. While Ukip has consistently polled close behind Nick Clegg’s party since the 2010 election, this appears to be the first time it has actually closed the gap overall. (One YouGov poll last year put them ahead among 18-24 year olds, but not overall).

As with any unusual result, it is worth noting that this could be an outlier. A Populus poll in the Times (£), also out today, keeps the Lib Dems safely in third place with 11 per cent of the vote.

However, it would be foolish to write off the result entirely, given that this has been on the cards for the last six months at least. In some ways, it is hardly surprising. The Lib Dems have traditionally been the beneficiaries of protest votes from those unenamoured with the two main parties, a support base it lost when it entered government. While many disillusioned Liberal Democrat voters went to Labour, Ukip benefited from those seeking a more anti-establishment alternative.

Conversely, Tory right-wingers frustrated at the perceived softness of their party in coalition may also be switching allegiance. As Antony Wells explains at UK Polling Report, there may be some more immediate factors too:

A third, more short term cause is probably the granny tax: we’ve seen significant drops in Conservative support and increases in support for UKIP amongst over 60s since the Budget and older people have always been by far the most likely group to vote UKIP.

It is certainly a boost for Farage’s party ahead of May’s local elections, though it remains unlikely that this will be translated into seats in parliament in the next general election. However, as my colleague Rafael Behr argued last year, increasing support for Ukip could shape future policy, particularly on Europe:

One factor that could really change the dynamic is the performance of Ukip - or rather, Nigel Farage's party's anticipated performance in 2014 European elections . . . Conservative strategists are, apparently, very worried about what that might mean for a poll that is due just a year before the next general election. It is feasible to imagine that, come 2014, Cameron will be more afraid of Farage's populist, nationalist agitation beyond the gates of his coalition than Clegg's cosmopolitan Europhile hand-wringing within.

It is entirely possible that Ukip will not sustain its lead in tomorrow’s YouGov/Sun poll – but this is a significant vote share for a minor party, and clearly, it cannot be entirely dismissed.

