Best known for Blue/Orange, his wonderful play about psychiatry, racism and schizophrenia, and an excellent movie adaptation of Ian McEwan’s Enduring Love, Joe Penhall returns to the theatre with a really enthralling dramatised debate about the ethics of inventing new weapons of destruction - masquerading, too, as a heart-felt play about two brothers.

Chippy, chunky Tom Hollander and the more languorously epicene Julian Rhind-Tutt, best known these days as the tousle-haired Mac in Channel Four’s Green Wing play the brothers in question: Ned (Hollander) is an engineer who has designed a new military technology programme, complete with surveillance cameras, that might well change the whole landscape of modern warfare; he is frightened by this prospect, and the likelihood, which accumulates in the play, that he will have no rights of ownership or control over his invention.

Dan (Rhind-Tutt) is a dentist with a side-line in cosmetic surgery who is also more susceptible to the reasonable claims of a general morality by virtue of having children, although a later conversation with an interrogatory man from military intelligence, the pink-shirted, dapper Brooks (the always excellent Jason Watkins), suggests he has a flimsy understanding of his wife’s dignity as an employee: “Does she work?” “No.” “What does she do?” “She’s a primary school teacher.”

In a way, Penhall picks up on a subject that has been a live issue since Bernard Shaw’s Major Barbara, where the ethics of an arms manufacturer are judged by the social good his wealth might create. But today the debate right across the sciences has moved on to worry about whether we have too much knowledge for our own good and to what extent the race for technological supremacy results in a quickening of political tension and a race towards the abyss.

Ned’s invention is one of “unmanned air vehicles,” known as drones, no longer needing satellite navigation to find their targets or gather enemy intelligence. The “reality” argument against Ned’s onset of anxiety about such a patent falling into the wrong hands is powerfully stated by Rhind-Tutt’s fellow Green Wing star Pippa Haywood’s commercial director.

Haywood’s bright and breezy, grey-suited Ross challenges Ned’s claim to intellectual ownership of his research against those of the Ministry of Defence. If you are in effect employed as a scientist by the government, to what extent can you claim your work as your own just because you start to feel queasy about its consequences? It is a fundamental question of our times, but Penhall also remembers his theatrical duties by writing a sparkling conflict between the brothers which climaxes in a very funny fight over a curry supper.

Hollander is on fine form, charting his physical decline into principled eccentric with a blazing sense of the human values his professional dedication has undermined, as well as that odd, slightly manufactured croak in his voice that suggests he might turn from a frog into Judi Dench at any minute. Rhind-Tutt’s slow burn playing and disapproving looks are a joy in a generally well acted show. Roger Michell’s precise and engaging production talks a good talk and is cleverly designed by William Dudley on a traverse stage that becomes a glass-walled aircraft hangar with an aeroplane motif catchy enough to adorn any young boy’s bedroom duvet.

- Michael Coveney