Sinead Morrissey’s On Balance, which has just won this year’s Forward prize, is a collection that keeps extending itself and that shares many of the satisfactions of fiction, memoir and history (there is an especially arresting poem about a model of Napoleon’s horse, another fine poem about the aviator Lilian Bland and an astounding poem based on a garish photograph of tsarist Russia). Even the poems that cross the finishing line with a flourish are open-ended, leaving one with the sense that there will always be more to say, and this is because Morrissey is possessed of her own invigorating brand of Irish fluency and an imagination that never closes.

On the subject of balance – there is always the likelihood that the world is about to tilt. The Millihelen (the poem that launches the collection) means (I had to look it up) “a unit measure of pulchritude, corresponding to the amount of beauty required to launch one ship”. A natural performer on the page, Morrissey holds us here with a feat of suspension, of literary engineering. This is a phenomenal performance: a single sentence, no full stops, a steady push out into the water – I take liberties in interrupting its flow to lift out these lines:

grandstand of iron palace of rivets starts
moving starts slippery-sliding down
slow as a snail at first in its viscous passage
taking on slither and speed gathering in
the Atlas-capable weight of its own momentum
tonnage of grease beneath to get it waterborne

She describes an event that one has witnessed but, without the detailed evidence of her poem, would have judged indescribable. She takes on the “tonnage” lightly, steering the poem to its close. But in another sense, the voyage has scarcely started. We wonder about the “ladies lining the quay in their layered drapery/touching their gloves to their lips” and their untold stories, their romances.

Other poems are anchored by family. There is a touching sequence about her grandfather, Collier(see below). He followed the horses but never placed a bet; fantasy wins furnished his life. The imagined improvements were humble – tea cosy, boots, a pigeon cote – and the writing about him is unprecious too. There are beautiful companion piece family poems about the importance of play.

The Rope describes the bond between siblings and Very Dyspraxic Child is about a boy’s brave loyalty to Batman. Child’s play is seldom child’s play to write about. And then there is the splendid title poem, taking on Philip Larkin, in which Morrissey arraigns him for his sexism in Born Yesterday (the poem written to mark Sally Amis’s birth) in which he wished her “dull” for the sake of happiness – playing bad fairy. She ends with this rebuke:

I wouldn’t let you near
my brilliant daughter –
so far, in fact, from dull,
that radiant, incandescent
are as shadows on the landscape
after staring at the sun.

The stinging spirit of this is wonderful. But it is Nativity that is the multi-tasking show-stealer. I love this poem. It starts as a sympathetic record of a school nativity play but then, by the second verse, has evolved: she casts the headmaster as an almost comically biblical figure. Morrissey knows how the story of the nativity will make every parent think. And she ends with a funny, moving, nerve-racking admission about the primary school children she watches: “whose frankincense we breathed when they were born” admitting that, as parents, we don’t know “what the instructions are – we’ve left them in itchy kneesocks, holding up a sign – or how it will end.”

• On Balance by Sinead Morrissey is published by Carcanet (£9.99). To buy it for £8.49 go to guardianbookshop.com or call 0330 333 5846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99

Collier (an extract) by Sinead Morrissey

Though he never once placed a bet, my grandfather
sat in his chair every day and picked out winners:
Larkspur, League of Nations, Isinglass, Never Say Die

in the 2.30 at Epsom or Newmarket.
He’d follow their dips and peaks, ingesting the painfully
difficult newsprint on off-work afternoons,

or he’d rely on the tug-at-his-sleeve of instinct:
his grandmother’s Romani nous with horses, his blacksmith-
father’s apprising sense bred into his muscles and veins…

And so his damaged house filled up with winnings:
tickets to a race, pairs of boots to choose from,
a tea cosy from a shop, a pigeon cote out the back,

and after each spectacular nose-across-the-finish-line
outsider made him rich (which happened twice)
he’d sit and eat his wedding supper over again in his imagined
life: ham on the bone; salmon, roast beef, egg-and-cress; a cake.