In looking at the often anarchic inner-workings of a the 1974-79 hung parliament, writer James Graham asks an interesting question about the purpose of the party with minority rule: what can they actually do? By the end of This House, a play packed with one liners and David Bowie tunes, it seems Labour’s most significant achievement is keeping the opposition out.

This theme is best explored in the second half of this 2 hour 50 minute long play that begins with an excessively lengthy but funny first half, which usefully sets up the procedures (some of them completely archaic), that get the political whips all in a tizz. But it gradually becomes increasingly urgent and we see the whips are on a mission with some pressing short term goals. The question that lingers over the production is who or what they’re on a mission for.

We join the whips as the Labour whips explain they need an equal number of MPs in the grounds as the opposition and they need the majority of those MPs to vote with them. As the years go on, they face rebellion in the ranks, an unprecedented number of deaths, sickness and injury, all of which put more and more pressure on these salt of the earth boiler-room workers. We see the rough and ready Labour whips mock their coiffured Tory conterparts in the same breaths they discuss the one woman among them. Their banter is sharp, surprisingly friendly, full of pretence and at times, brilliantly entertaining. But as the sick and injured are dragged in to cast their vote, there seems to be something amiss. At the most horrendous scenes, everyone’s still laughing and I’m left thinking surely there’s supposed to be a change in tone?

It comes eventually, when Labour are being booted out and the most devout among them is suffering the worst. At this point one particular Torrie displays a touching act of grace and the humanity involved in running parliament rings out with the strength of a choir. But for me it’s too late. Most of these points have been established before and they’re being hammered home in the final minutes. It’s a nice conclusion but not an affecting one, the humanity of these politicians, though moving, leaves little to chew on.

You can see this more clearly when the writing expounds a real issue and soars all the more for it. It’s not the humour that surrounds the deputy Tory whip who comes from a family of tailors on Saville Row, but the idea of a female MP discovering her position in a boys club, or another choosing to vote in the best interests of her constituency even though it puts her party in jeopardy.

I know Graham’s intentions aren’t to focus on the politics (because he told me) but there isn’t enough about policy here and when there is, this play becomes momentarily superior to much else that’s been on offer this year. The few brief mentions of North Sea Oil for example, are tantalisingly good, it’s a shame the prospect of impending economic power isn’t explored in more depth, particularly for an audience who know what happened next.

While a lot of this production should be applauded:it is funny, it is sharp; it still isn’t as probing as it could be. Instead, Graham, together with director Jeremy Herrin’s clever decisions around the movement and the music of this show, looks at the people behind the politics and the events that drive their most interesting moments. The problem is, no one’s grappling properly with their relationship to the public, which in theory is ultimately driving them, right?

This House runs at National Theatre until December 1st 2012