Why it was done   How it was done "I got the idea from just being in cabs," says Amelia Bullmore with disarming simplicity. Black Cab is her brainchild, and she has written three of the films in the series (Busy Body, Marriage Guidance and Tom & Marianne).         "I kept having the most amazing conversations with cabbies - complete strangers. It was possible to tell them anything. It's the perfect set-up for human interaction - and the containment of it only makes it more intense. You also know that what you say in a cab will have no consequences, because you'll never meet again. It's like time out from your real life."     "We all need to off-load things onto other people," continues Bullmore. "Talking to a cabbie is like therapy - only much cheaper. We want a sounding-board for our ideas, but without any hellish repercussions."         These were the very elements that appealed to producer Chris Clough, whose credits include Ballykissangel and The Bill. Taking a break on a chilly February day's shooting in East London, he reckons that "the idea works because it's set in such a small, theatrical space, in which two strangers are put in close proximity. It's very intimate. People open up more because there's no one else listening."     "The fact that the two protagonists don't know each other only adds to the drama. People will tell total strangers all sorts of intimate secrets that they'd never tell anyone else." The series gives five writers the chance to make their television debuts. "Primarily, we see it as a launch-pad for writers new to television," says Clough. "It's about encouraging individual voices rather than making writers conform to a well-established series with inherited characters."         Jake Lushington, co-producer, emphasises that the writers' creativity flourished precisely because they were given well-defined boundaries in which to work. "We wanted a wide variety of stories, but we also laid down very strict guidelines. The cab had to be central and in shot at all times. We didn't, for instance, want any unbelievable stories, nor did we want to make any grand cinematic statements about London. London is there in the background, as dreary or as beautiful as it is in everyone's experience."     "Each film is a definite journey and all have a structured precision about them. Writers would complain that they couldn't fit a three-act story into ten minutes, but in fact creating a full story - complete with a set-up, middle and resolution - gives each film its depth and power."                 © World Productions 2000 / All rights reserved; Photographs © BBC, Channel 4 and World Productions No material from these pages may be reproduced in any form without the permission of the copyright owners.