In the final episode when the girls steal the car. The registration begins with a T. When they're driving up to London, the registration letter has changed to S, with a completely different registration plate.
At the end of season 2 Stella discovers she's pregnant and that the baby has got to be Nathan's. However, at the beginning of season 1 Stella told Kim that Nathan can't discover she's on birth control because he's been snipped.
Kim: So that's how it is then? You call, I come running. You say jump, I say how high? Translating for French guys, spending my mum's credit card when you could be with someone else. Name something you've done for me. One thing. One SODDING thing.