Harriet:

The result is that in mid third season, which is where I'm at, they've had to split the crew between two ships who get alternate episodes.

...which happened to confuse the heck out of me, since I happened to miss that particular episode; I just got the impression that the Beeb had dropped the stack of tapes, and not bothered to sort after picking them up. Having read an "upcoming episodes" guide in an old magazine to work out what I'd missed, things became *much* clearer.

steve