At the start of the scene in which Tanya steps out of her limo to pet a girl's dog, a closeup reveals the film crew reflected in the side of the vehicle.
Miss Wilderspin says to Peter, "I see you attended Christ College. Oxford, or Cambridge?" There is no 'Christ College' at Oxford or Cambridge, though there is a Christ's College at Cambridge and Christ Church at Oxford. From other remarks made by Miss Wilderspin we are led to understand she is familiar with Oxford and Cambridge and very possibly went to one of the universities herself. So it is unlikely to be a mistake made by the character.