Bill Nighy does a mean line in bumbling. In fact he’s just about cornered the market in it lately, the rightful heir to John Le Mesurier’s character in Dad’s Army. In The Girl in the Café, Bumbling Bill virtually stumbles his way to oblivion, almost disappearing in a mess of “hmms” and “aaahs” and mumbles and apologies and nervous tics.

Which leads straight into the first of this show’s many stretchings of credibility. First, that an attractive woman who looks about 20 years his junior, would find him in any way appealing when he happens to sit across from her in a café, bumbling and apologising, in his boring office blue suit. Then there’s the fact that someone so apparently woolly-minded is a high-flying economics expert on the Chancellor of the Exchequer’s team. Next is the forced plotting indulged in to effect the meeting of the odd couple – someone so high powered and extremely busy has taken time off to seek out a greasy-spoon caff for a cup of tea, and there’s only one place to sit – opposite the waiting female love interest.

And all that’s only in the first scene. The unbelievable quotient then proceeds right to the top: a supposedly naïve young female ex-con easily finds herself attending a G8 summit in Reykjavik, without any hint of a security check, and pulls up the Chancellor on some of his policies in front of the German leader in a canteen. Then, even after such a major public embarrassment, she gets to dine, as Bumbling Bill’s partner, with the Chancellor and Prime Minister and, in an address which sounded like it had been crafted by a skilled politician’s speech-writer, tells them what’s wrong with their whole approach to Africa (the show’s part of the BBC’s Africa season). Oh and she isn’t kicked out until the speech is nicely finished, and they’ve all listened.

Finally, her reprimand of the government results in major policy change. The British PM and Chancellor then make the rest of Europe follow suit. We’re left to imagine for ourselves the closing scenes of happy Africans tucking into endless feasts or looking on blissfully at their now healthy frolicking children, in a land free from disease, free from fear, while triumphal music plays and benign European politicians grin smugly and wave at the cheering people.

The whole programme looked like a contrivance written to a brief, something like “A naïve and humble little person sees straight through all the political bullshit and influences European policies on Africa with her simple view of the truth. Something terribly English, touching, romantic, but it has to be really about the big problems facing Africa.”

The excellent acting, especially from Bill Nighy and Kelly Macdonald in the lead roles, was like seeing Gordon Ramsay politely doing his best with poor quality, synthetic ingredients, keeping the insults at bay because it’s for a good cause. But good causes don’t necessarily have to mean poor products, do they? We are much more likely to be forgiving, of course, and perhaps that’s why this programme’s unbelievable content was allowed to survive through to broadcast. The story looked as if it had been rushed, and a bit forced, in order to make its point, which seemed to be something like “forget all the complexity, you have the power to change things in Africa, just do it. Now.” Saint Bob in the form of a BBC drama.

Obviously if it makes even a small fraction of the difference Bob has made, it will have been worth it. But that doesn’t mean it can’t also be assessed as drama, which is what it is.

The bumbling male is familiar territory for Richard Curtis, the man responsible for the most successful romantic film comedies produced here in recent years. Hugh Grant in Four Weddings and a Funeral is a clear forerunner of Bill’s character. Curtis’s application of the type to a worthy drama attempting serious points about Africa produces a kind of discomfort, though – in me at any rate. This is light comedy of the Four Weddings … and Love Actually school: sentimental, cutesy, not too demanding, often sold as “touching and funny”. The serious points it was trying to make sat uncomfortably in this environment. On the other hand, of course, casting such an important issue in such frivolous form might well introduce it to an audience who would otherwise be indifferent, and if it works then good luck to it. The patronising, even deceptive, aspect of the sugar-coated pill perhaps don’t matter here, in relation to the possible magnitude of the effect. Criticising it as drama comes to seem rather petty if this is the case.

So why don’t we pack our bags and go home?