However, there is an emerging threat to this generally courteous and professional relationship. It is not that there are fundamental disagreements over such issues as the NHS- although there are. Neither is it because of David Cameron's determined leadership of the No-to-AV campaign. It is not even because the Conservatives are focusing on a numbers game in immigration, although that is in the view of many Liberal Democrats- not least Vince Cable- completely counter productive to a disciplined and organised immigration policy. No, the emerging problem is outside the coalition.
The remarkable surge in the support for the nationalist, Euro-sceptic, True Finns in the Finnish General election is reminding some political observers that Britain too has a significant Euro-sceptic party, the shape of UKIP. Thus far, UKIP has only been able to achieve success in the European elections. It has yet to gain significant numbers of councillors, and it has no MPs, MSPs or AMs. Yet, the latest opinion polls, ahead of the local elections in May, show a significant growth in support for Other parties- some of this is clearly an uptick in the nationalist parties, the SNP and Plaid Cymru, but it may also reflect a growth in support for UKIP. Such a growth would certainly inflame those on the Tory right who have never supported the coalition.
The question is whether the Conservatives would lurch to the right, in a bid to crush a potential insurgency from UKIP, or whether they would maintain the relationship with the Liberal Democrats. From the point of view of political journalism, the temptation would probably to highlight the "threat" from UKIP, particularly if the switch to AV was supported by the referendum. On the other hand, expectations for the Liberal Democrats are now so low that even survival as a force in local government will be seen as an achievement. Yet, it may indeed be that Labour have overplayed their hand, and their breathtakingly patronizing campaign, which seeks to suggest that Lib Dems are "really" Labour voters anyway, may yet reprieve the junior coalition party. The question then will be more complicated than a straight swing to Labour, but different messages from different parts of the country.
In fact I expect that there will be a very mixed message from the different local and national elections, and one that the coalition as a whole may find reassuring. Labour may not find the going in Scotland entirely to their liking, although I fear that the Lib Dems will be most badly heart north of the border. Elsewhere, any progress for UKIP will be interpreted as a threat to the coalition, although even under AV, UKIP will probably toil to gain a single Westminster seat.
The True Finns may take some of their inspiration from UKIP, but even a few Council gains will not put UKIP in the same league as their Finnish colleagues. The real battle remains between the coalition and Labour- and Labour may not get things all their own way.