Negotiating the ups and downs of a long-term relationship is one of the main themes in Andrew Fleming’s latest comedy, Ideal Home. The couple in question are TV Chef, Erasmus Brumble (Steve Coogan) and his partner, Paul (Paul Rudd), who is also the Producer of Erasmus’s cookery show, set in Sante Fe.

Their lives are turned upside down when Coogan’s estranged 10-year old grandson, Angel, (Jack Gore) gate crashes one of their decadent dinner parties, after his no-good Dad has been sent to prison.

With Angel’s father locked up, Erasmus and Paul must decide whether to hand him over to child protection services or take on the challenge of unexpected parenthood – they plump for the latter.

It is a paint-by-numbers plot in which the audience is pointedly given back story to link the ensuing scenes. Fleming also wrote the script which does contain some witty side swipes when the two protagonists are in full throttle bicker, but mostly the gags are easily anticipated or feel past their sell-by date.

Coogan and Rudd are skilful comic actors who individually command centre stage, so casting them as a squabbling, party loving couple, who clash when their relationship comes under the microscope, could have produced some top-notch comedy drama. Unfortunately, no magnification is required, as their characters and personality ticks are so over the top, they are bordering on caricature.

Despite this, there are some moments to savour. Maximum cheese is served up in a pastiche of a cheap cookery show, and as the preening celebrity chef, this is classic Coogan territory, which he delivers with ease. In one scene he slowly falls off his horse, it is old school slapstick at its best and Coogan’s timing is spot on. However, when Erasmus is ‘off duty’ he remains a vain, two-dimensional megalomaniac. As a result, when he appears to be mellowing towards his grandson, it doesn’t ring true as a genuine character progression.

Hipster Paul, is the most grounded of the two, and Rudd is given some dramatic scenes he executes well as he gradually learns to man-up to his parental responsibilities. There are some tender exchanges that play out well and provide a naturalistic breather, that the overall film lacks. Ultimately, even though Rudd plays the straight man to Coogan’s clown, the two of them still struggle to be convincing as a couple.

A contradiction that never gets resolved is that the supporting characters don’t appear to care that Erasmus and Paul are in a gay relationship, yet the pair themselves, almost entirely identify themselves by their sexual orientation, constantly riffing and joking about it.

Highlighting the emergence of a new family unit by showing same-sex couples raising children, is rich and interesting turf to explore, but Ideal Home, misses the mark, despite its best intentions.