Leaky - update
He had accidentally pulled the basin and bidet waste pipe out of the main stack when fitting the basin, so all waste water was pouring down the inside of the house. Luckily I don't wash very often! No water damage visible inside the house, and porch brick wall now drying.
Then the bidet started leaking, so he came back another day to fix that - the bit on the bottom wasn't screwed tightly. (technical term!)
Now it's just a corner of the shower than leaks intermittently onto the floorboards. I think I will just squirt more sealant on myself. Want it all to be right before getting a carpet laid in there (yes, I like a carpet in the bathroom. I don't piss all over the floor like some people!)
The main bathroom is still to be done, but another plumber says we need a bath with pre-drilled holes for the taps, as the one we have bought [and is waiting in the garage] has no tap holes (because of the odd modern tap we've bought for it - a large mixer tap and a shower head that slots into the bath top next to it. So the bath in the garage will probably end up on eBay like the old fittings from my bathroom (got £167 for them!).