Marissa Platting was the social worker assigned to Kevin Ball and Veronica Fisher when they were involved in fostering and possibly adoption. She appeared in Series 2.
Though little is known about Marissa, she continually appeared flustered and disorganized to the extreme. She also spoke particularly candidly about her work. She was even involved in forcibly removing Eric Tatchell, the boy Kev and Veronica had fostered with police aid, only to realize they had mistakenly removed the wrong child from the wrong family.
As a symptom of being over worked and disorganized Marissa mistakenly called Kevin "Kelvin" instead. This lead to many viewers wrongly assuming "Kev" was short for Kelvin.