The Upper Hand

Joanna and Tom age in a somewhat "elastic" fashion throughout the show; made more complicated by the fact that it does not appear to take place in real time. Joanna is said to be 11 in the first episode and celebrates her 12th birthday later in the series, before rapidly progressing through her teens. In the series four episode "Tunnel of Love", set exactly four years on from episode one (although airing less than three years later), Jo has long since turned 16. She then appears to remain 16 throughout series five, regularly seen in school uniform panicking about exams, before suddenly becoming an 18 year-old university student in series six. In series seven, Charlie states that Jo is 20.

Tom, who is seven in series one, seems to age more consistently initially, and is 11 in "The Tunnel of Love". However, he suddenly becomes 13 in series five (while Jo does not age at all) and ages again to 15 in series six (coinciding with actor William Puttock's voice breaking and him experiencing a growth spurt).