One might have assumed that the Scottish election would be the high-point for devolved drama in this election cycle, but yesterday the Welsh Assembly, of all places, tried to top it.

What happened was that the newly-minted Assembly failed to elect a First Minister.

How did this happen? At the elections, Labour lost a seat (a spectacular win in Rhondda by Leanne Wood, the Nationalist leader), taking them to just 29 seats in the 60-seat chamber. Plaid’s one gain put them on 12, the Tories lost three and slipped into third with 11, UKIP won seven, and the Liberal Democrats just one.

It was a disappointing night for the Conservatives – who had been hoping for gains, including the last Lib Dem seat whose Westminster equivalent we took last year – but more importantly it cost Labour their majority. Labour and Plaid then each lost one AM to serve as the Presiding Officer and her deputy.

But Labour didn’t make any arrangements with the other parties to make sure that Carwyn Jones, their incumbent First Minister, was re-elected, presumably because there isn’t a credible alternative government in the Assembly.

Yet when Plaid put their leader forward to contest the position, every single Conservative and UKIP AM rowed in behind her. Only Kirsty Williams, the sole surviving Lib Dem AM, brought Jones to a tie.

Votes are taken by the Presiding Officer (speaker) one by one in alphabetical order. If Williams had abstained, the Assembly’s two right-wing parties would have elected a very left-wing, stridently nationalist First Minister.

Did they know which way Williams would jump? If not, it was surely an extraordinarily irresponsible thing to do.

In truth, despite this embarrassment Labour’s reading of the arithmetic of opposition is broadly correct.

For all that Wales employs proportional representation, Plaid Cymru take a decidedly adversarial approach to parties on the centre right. Wood has ruled out any deal whatsoever with either the Conservatives or UKIP. That fact is Labour’s ace in the hole.

It leaves the 18 right-leaning AMs with no reason whatsoever to back Wood. Her administration would give them nothing. It would be a Nationalist minority government daring Labour to join with the right and vote down ‘progressive’ legislation.

Yet it also leaves Wood precious little leverage against Labour, which is probably why they were so complacent going into yesterday’s vote. Having poured scorn on all her potential coalition partners, the Nationalist leader’s only route to the First Minister’s office relies on the votes of right-wing AMs who don’t appear to have any rational reason to provide them.

One can see why Labour didn’t think that possibility likely before yesterday afternoon.

The party who do benefit, of course, is the decimated Lib Dems. Williams’ vote is all that kept Jones in the running yesterday and if UKIP and the Conservatives were to repeat their stunt she, who votes near-last, would be gifted a huge amount of influence.

I understand the desire to give Jones a bloody nose. Labour has misgoverned Wales, and Jones has completely bought into the soft-nationalist, blame Westminster defence so popular with ailing devolved regimes. His demands for an end to the sovereignty of Parliament – the foundation stone of our constitution – warrant the odd (political) kicking.

But we should have learned the lesson from when the Scottish Conservatives propped up a minority SNP administration in 2007-11: it never pays to be complacent with nationalists.

It is obviously much to be welcomed that Plaid have not had the success of their Scottish counterparts, although this election was a fillip for them. But that is no reason to gift them the profile and resources of the Welsh executive for five years.

Some might argue that it would be wrong to keep an incompetent unionist regime in office if there were a pragmatic, competent Nationalist-led alternative in the wings. But this is Plaid, whose only criticisms of Labour’s left-wing misrule in Wales are that it has not been left-wing enough and that too much of it has been conducted in English.

Perhaps it will turn out that this is in fact a master-stoke by Davies, and he walks away with real concessions. But Labour have always been happier working with the separatist left than the unionist right, so they may well seek to buy off Wood rather than her unlikely allies – all whilst promising the one-seat Lib Dems whatever it takes to keep them on side.

Yesterday’s vote provided an afternoon of high drama and embarrassed a complacent administration. Those meagre rewards do not, yet, seem to justify the risk the Tories took in backing Plaid.