A formidable obstacle to a Lab-Lib coalition
The enduring hostility between the two party's activists could scupper a deal.
As the Lib Dems' poll surge shows no sign of abating, Labour ministers are beginning to dream again of a progressive coalition between the two parties that allows Gordon Brown to remain prime minister.
But one formidable obstacle to any political cooperation remains the fierce hostility between the two party's activists.
The leaflet below (from the excellent The Straight Choice) is an example of the sort of crude tactics Labour often uses against the Lib Dems at a local level. It combines an attack on the party as "soft" on murderers with an assault on the Lib Dems' support for the European Union.
The leaflet, distributed on behalf of Labour MP Roger Godsiff, even echoes Thatcher in declaring "no, no, no" to the European Court's ruling that the UK's ban on prisoners voting is illegal.
The ill feeling towards Labour that such tactics encourage wouldn't be such a problem if it wasn't for the notorious "triple lock" that binds Nick Clegg in any hung parliament talks. Imposed on Paddy Ashdown in 1998, it requires a Lib Dem leader to seek the approval of members and MPs before entering into a formal coalition.
The smear campaigns that both parties have run against each other mean that few will be willing to kiss and make up after 6 May.