The rapid decline of the Liberal Democrats in the polls has led to an understandable outbreak of schadenfreude among many Labour supporters. However, the knowledge that a total eclipse of the party would see the Conservatives picking up a considerable number of small-town and suburban seats from the Liberal Democrats casts something of a cloud, depending on how one sees the electoral arithmetic and how much worse than this coalition an all-Tory government with a small majority might be.

Using a ‘dumb’ uniform national swing calculation and an approximation of current average opinion poll ratings (Conservative 40; Labour 42; Liberal Democrat 10) one would see the Conservatives gain 28 out of the current 57 Liberal Democrat seats and Labour gain 18. Of the remaining 11 seats, there would be several rightwingers (Nick Clegg, Norman Lamb, David Laws) and several leftwingers (Charles Kennedy, Menzies Campbell, Tim Farron), reprising the 1950 situation when, despite being reduced to nine seats, the Liberals were still ideologically split down the middle.

The size of the Liberal Democrat contingent in the next parliament may owe more to trends in particular regions and types of seat. They are dependent on the south-west (15 seats) and Scotland (11 seats) for nearly half their MPs, and will suffer if one or other of these areas turns decisively against them. Using regional breakdowns of Ipsos MORI figures from the second half of 2010 (when the party had not reached their recent lows) would give the Conservatives 15 and Labour 10 of the Liberal Democrats seats, with 32 seats retained.

The other dimension is the social make-up of the seats that the Liberal Democrats won in 2010. The most vulnerable of these are the 10 seats with large proportions of students and liberal professionals, many of which returned Tory MPs until the 1980s and then were Labour until 2005. Several MPs in these seats (for instance, Cambridge and Manchester Withington) were, understandably enough, tuition fee rebels. Labour should be confident about picking off seats in Norwich, Manchester and north London purely on the basis of reaction to Liberal Democrat betrayal and general opposition-mindedness among these electors – several of these areas swang sharply against Labour even in 2001. If the swing against the Liberal Democrats is concentrated in these areas (plus working-class seats like Burnley), and weaker in the suburbs and smaller towns that the Liberal Democrats hold against the Conservatives (such as Sutton and Cheam or Taunton Deane), Labour could even be the net beneficiaries of a less-than-total Liberal Democrat slump.

However, as well as the direct Labour danger to these constituencies, many of the seats they hold against the Tories are in areas where they have squeezed down the Labour vote. In 1997 Eastleigh was a three-way marginal; there is a latent Labour vote in several towns and suburbs which may pop up if the Liberal Democrats are insufficiently distinct from the Tories. However, some local authority by-elections in the south of England suggest the Liberal Democrats can still win large swings against the Conservatives. The political logic to this may be that in May 2010 voters wavering between Liberal Democrats and Conservative plumped for the Tories because they believed the Liberal Democrats would keep Labour in power. Now this is not a consideration, the Liberal Democrats may gain votes from the Tories. In some seats this might compensate for the loss of previous tactical votes from Labour supporters.

The next election will not take place on the same basis as the 2010 election. One change will definitely happen, namely, a new set of parliamentary boundaries based on 600 constituencies and new rules for how they are composed. This change is potentially highly destructive to Liberal Democrat chances. Democratic Audit’s model of new boundaries showed the Liberal Democrats taking the largest proportionate hit of any party, dropping from 57 to around 45 seats if votes were cast exactly as in 2010. The reason for this is that Liberal Democrat seats tend to have smaller majorities, and are also geographically isolated – boundary changes bring in neighbouring territory where they have few votes. In some areas, there are potential conflicts between Liberal Democrats incumbents (like Charles Kennedy against Danny Alexander) or awkward intra-coalition tussles with Tory MPs whose seats are merged into Liberal Democrat ones (as in Cornwall and Mid Dorset).

The party’s hope is that the damage from the boundary changes will be mitigated by a Yes vote on switching to the Alternative Vote. AV would undoubtedly mean more Liberal Democrats in the next parliament than under first past the post. The effect may be relatively small in the Liberal Democrat-Conservative marginal seats, because as soon as the coalition was formed there was a steep drop in the proportion of Labour voters who would give a second preference to a Liberal Democrat, but one must assume it will be positive. A potentially interesting project if we do get AV would be ‘rate my Liberal Democrat’ – to see according to measurable criteria (eg the tuition fees vote) which of them are worth a Labour voter’s second preference and which are not.

Conservative voters, however, may be more willing than in the past to help the Liberal Democrats with second preferences, and perhaps this could salvage a few seats from Labour. AV could potentially widen the fault lines within the Liberal Democrats, because different MPs will have to appeal to different sources for second preferences.

Labour need not be very afraid of a Liberal Democrat wipeout. The net gain for the Tories, if it happens, is relatively small and unlikely to be crucial in terms of parliamentary arithmetic as long as Labour is making some net progress against the Tories. If polls and midterm elections show the Liberal Democrats heading for oblivion, this might increase the leverage of the more progressive elements in the party to press for better outcomes within government and keep the option of a Lib-Lab coalition open following the next election. The more severe a defeat is inflicted upon the party, the weaker the influence of the Orange Bookers will be in future. While the next election may well see a reversion to two-party politics, this will probably be only a temporary interruption to a long-term trend. By all means pass the popcorn and enjoy the electoral destruction of the Liberal Democrats in 2011, but remember that we may need them, and they may need us, in future, and some time or other both deficit hysteria from Liberal Democrats, and pointing and laughing from Labour will have had their day.