In 2007, Andy Hamilton and Guy Jenkin abandoned the conventions of a tightly scripted sitcom and took a more fluid approach to mining laughs in the breakout hit Outnumbered.

While the adult characters' lines were committed to the page, the young actors were allowed to improvise around suggestions from Hamilton and Jenkin, and consequently delivered natural performances, reacting instinctively to set-ups and punchlines.

The writer-directors adopt the same winning recipe for this uproarious feature film debut, an ill-fated family road trip laced with absurdity that touches the heart and tickles the funny bone.

Once again, it's the younger cast who scene-steal with aplomb, explaining why a bout of car sickness is a source of joy ("It's like being a fountain!") and succinctly distilling the anguish and betrayal of parental infidelity into a single throwaway line: "Dad had an affair with a Paralympic athlete with one foot."

That's not to say that Hamilton and Jenkin short-change the rest of the ensemble cast including David Tennant, Rosamund Pike and Glaswegian firebrand Billy Connolly.

They snaffle a generous smattering of belly laughs too, like when Connolly's cantankerous grandfather tries to explain Hitler's seizure of land in terms a bairn might understand: "Like Monopoly, but with more screaming."

Gordie McLeod (Connolly) is poised to celebrate his 75th birthday in the Scottish Highlands.

His self-obsessed son Gavin (Ben Miller) is hosting the lavish party to impress the neighbours and hopefully secure the captaincy of the local golf club.

Gavin's long-suffering and neurotic wife Margaret (Amelia Bullmore) remains in the background, occasionally exploding with pent-up rage.

As the party beckons, Gavin's less successful brother Doug (David Tennant) and his wife Abi (Rosamund Pike) arrive with their three children in tow: 11-year-old Lottie (Emilia Jones), who scribbles repeatedly in her notebook so she can remember which lies she is supposed to tell; six-year-old Mickey (Bobby Smalldridge), who is obsessed with Vikings; and five-year-old Jess (Harriet Turnbull), whose best friends are two rocks christened Eric and Norman.

The birthday celebrations are unexpectedly thrown into disarray and a media scrum descends on the family's doorsteps along with an interfering Social Services officer called Agnes (Celia Imrie), who casts doubt on Doug and Abi's ability to nurture their dysfunctional brood.

What We Did On Our Holiday is a rip-roaring riot, laying bare the petty jealousies and deep-rooted fears within a family while dealing with serious issues through the unblinkered eyes of the three children.

Tennant and Miller spark a fiery sibling rivalry with excellent support from Pike and Bullmore, the latter proving that it's the quiet ones you have to watch out for.

Hamilton and Jenkin eschew cloying sentimentality in the film's tricky final third, striking a pleasing and ultimately winning balance between musing and amusing.

RATING: 8/10