The King’s Head Theatre on Upper Street is one of a series of venues which are playing host to Festival 46, a showcase of the best of new British writing. This week is the turn of Don’t Look Down, a one man show written by Giles Fernando and directed by Victor Correia, which probes the painful absurdities of ageing.

The show follows Max (Paul Casar), an accountant on the cusp of his fortieth birthday. The story is, in many ways, the familiar one of a mid-life crisis. There are the standard jokes about receding hairlines, encroaching paunches, fitness kicks and health scares. This is complemented by a stock of well-worn characters- a camp hairdresser, a snooty opera singer- that populate the periphery of the work. This isn’t necessarily a bad thing- Casar gets some well deserved laughs- but the audience knows it is on safe, familiar ground.

It is when the script departs from this path that it produces something of real interest. The way it deals with the body and its functions is particularly interesting. There is a fair bit of crass toilet humour (Casar seems to spend half the performance with his hand down his pants), but it serves not to garner cheap laughs, but draw attention to the frailty and hilarity of the ageing body. It is childish humour belying adult anxiety.

The plot verges on the unbelievable- Max loses his girlfriend and packs in his job to follow his teenage dream of becoming an Elvis impersonator. Often it feels like it is running away with itself, but once again flashes of excellence shine through. The feverish, breathless tone of the narrative, which plays out as a monologue from the main protagonist, is extremely effective in conveying his inner torment. The play’s end too, is startlingly abrupt and reaffirms our capacity to choose our own path through life, even when it seems as if we are powerless.

Casar as the only performer carried the show with consummate ease, able to mix humour and gravity, absurdity and thoughtfulness. He is particularly adept at inhabiting other characters in the narrative, which adds depth and counterbalances levity. This feverish pace, so important for the work’s tone, could have been slackened on a few occasions to allow some of its import to sink in.

Don’t Look Down is something of a mixed bag. What it lacks in polish and finesse it makes up in flashes of hilarity and moments of well observed insight. As part of what emerging British dramatists have to offer, it’s well worth a watch.

Don’t Look Down is playing the King’s Head Theatre until 29 July. For more information and tickets, see the King’s Head Theatre website.