It had to be VERY carefully scripted, so as to not produce the same effect on the populace, who heard it but couldn't see the screen, as the War of the worlds broadcast that caused large amounts of the USA to panic.
The scripting, presumably, being a narrator saying at the start "This is not real" ? (Sorry, I know nothing about this film. I just know that I'm as sick and tired of the snowman as its creator is.) --Vitenka
The Mercury Theater War of the Worlds said at the start that it was a Mercury Theater on the air production. This didn't help those who tuned in after the start. Likewise GhostWatch, a Screen One production and as such preceeded by the Screen One logo.
Yes, yes, I know (well, I knew the first one - I'd never heard of GhostWatch.) I was more saying "Aren't people stoopid" --Vitenka
During the part likely to cause problems, they had the two main characters chatting away in the background (would you like another cup of tea, dear? etc.). That way, the announcement that WW3 (or whatever it was) was starting couldn't be taken for a real announcement.
Ah, cause the problems. Anyone who hears a single announcement of MartianInvasion? of WorldWarThree and doesn't then, you know, check that it's for real deserves all the embarrasment they will cause. --Vitenka (And everyone else can enjoy the quiet amusement. Though call centre operators are likely to get snowed in)