Section 41 of the 1925 Criminal Justice Act prohibits sketching in court, so Coleman and her colleagues must scrutinise the scene and retreat outside to do their drawings.
In the past, Coleman has observed some dramatic reactions from witnesses but most are quietly miserable. "I've done so many witnesses crying," Coleman says.
To be a courtroom artist it helps to have a good memory for faces. Coleman works almost as a caricaturist, focusing on any particularly pronounced features of the subject. Rose West was "pretty easy to draw", according to Coleman, her body "a big circular thing - kinda lumpy". Justice Mantell was "lovely to do". His red robes, white hair and "benevolent" manner making him "just like Santa Claus".
Framed by the TV screen, Coleman's drawings may look small, but she works on 3ft canvasses. Providing picture stories for the 12.30, 5.40 and 10pm news means that Coleman can draw a witness in 10 minutes. For the West trial she used the same background for each image, superimposing different characters on to an acetate overlay. One of the advantages of the oil pastels she uses is that they are "thick as butter, so you can scrape them off to remove a person from a scene" and replace them with a new witness.
While the basic oeuvre is pastel naturalism, artists adopt different styles and materials. The BBC's Julia Quinlan uses pencils and "never gets her hands dirty", while freelancer Richard Cole's bold, cartoonish style is often commissioned for lighter news stories.
Carlton prefer Coleman to use watercolours, but given the choice, she would rather use pastels which make her work "heavier and more colourful - like an oil painting".
Some would argue that most courtroom sketches barely resemble their subjects. Yet, in her defence, Coleman points out that her drawings are often sold to barristers and judges. "They spend so long working on a case, they want something to remember it by," she explains.
Geoffrey Robertson QC has at least six of her drawings, including one of him cross-examining Princess Diana about the gym photos. Although the case failed to reach the courts, Robertson decided to buy it anyway.
Coleman frowns upon artists who "cheat" by working from cuttings, pointing to West witness Mrs Leach as an example of the dangers of this method. Leach had a stroke between giving evidence, which radically changed her appearance.
With cameras "going in everywhere", Coleman believes it won't be long before her work "dies out". Electronic media means that the archaic world of the courtroom artist is already changing.
For now, Coleman relishes the challenge of courtroom art and relaxes in her spare time by painting "decorative abstracts". At the Henderson Carter Christmas exhibition, these two styles are displayed side by side and for just pounds 1,450 you can buy The Ghost of Fred West, a weird hybrid of the two.
Coleman's work is showing as part of the Christmas Exhibition at Henderson Carter Art, Townmead Road, Fulham, London SW6 (0171-371 8676)Reuse content