[Steve in Pudsey]

On the other hand why should North West Tonight get it's own studio when BBC London no longer does?    Ideally both would have their own studios, but it just seems odd the BBC can afford a dedicated regional studio up in Salford but not in London.   

You could say that of almost every other region though. It's just an operational convenience to reduce crew costs in London that makes it possible to share, but the trade off is that London gets to use Studio B