Too late for me to edit...

I've just seen that UKBA added "* THERE ARE NO OFFICIAL OBSERVATIONS *" to my passport bio pages. This is why they retained mine, then. I'm not sure whether this is stamped purely because they were making an official check anyway and my passport is çlean, or because my passport is empty (unused). So they needed my actual passport, it seems (as well as my partner's). That said, what would they do with sponsors who don't have a current passport? So I'm not sure.

If it was me, I would be inclined to rearrange the FLR appointment so I could be there too, rather than risk a refusal or having to pay that fee all over again.