I still don't understand why Miranda believes that booking boxes at the opera and Test matches and gliding around cocktail parties should warrant an equal share in a business, but then she doesn't really have to believe it, does she, only assert it in a negotiation.
That was an interesting bit of scriptwriting. When Justin arrived in Borsetshire, he wanted an introduction to the 'right sort of people'. Lillian arranged it, just like Miranda did back in the day. Notice how (both times) once the deed was done, Justin was dismissive of the input and claimed that it could have been organised by any of the girls in the office.