From THE INTERNET MOVIE DATABASE:
The wonderful Bob Peck, stars in this mid-Eighties Nuclear thriller that was so popular when originally shown on BBC2, it was immediately repeated on BBC1 (an unheard-of achievement).
Peck is untouchable as the doubly-bereaved Ronald Craven, a good cop who is drawn in to a web of intrigue and nuclear paranoia when his environmental activist daughter Emma – a pre-Kilmer Joanne Whalley – is gunned down, notionally by a madman from Craven's shady army past in Northern Ireland. The plot thickens, a golf-mad CIA operative with the fabulous name Darius Jedburgh – Joe Don Baker excelling – enters, and the whole thing goes down from there.
What the magic rectangle was invented for.