Thanks for all the replies.
The bit about 'if the engine conked out, would we got down?' - in our particlar case, and on the way up, yes. On the way back home, no. By turning around, we actually flew into the worsening weather behind us, but luckily, we knew (well hoped anyway) that it would clear by the time we got back down to Barrow - which it did.
As for the other interesting bit, the bit about two pilots having a higher threshold of get-there-itis, I think this is totally true. If I had been flying solo, or with my mum for instance, I would have turned back when I first got those inklings of doubt, not half-an-hour later.
Interesting debate.