PS Since posting the above, I've rechecked my system's performance in Task Manager with this batch of songs, and find my memory was playing tricks.

CPU Usage leaps up to 100% and hovers there or just under until the song starts to play. On the other hand, the usage of physical memory is modest, with available memory dipping slightly, but hovering around 1/3 of the total 1GB.

So it looks as though I'm going to have to dig deep into my sporran and get a laptop with a much faster processor if I'm to get a quick response on a gig, but that I may not need to go over the top with memory capacity.

As it happens, my clarinet-playing colleague has a new laptop which we use on gigs, so mine is used for preparing songs and individual practice, and will only be used on gigs if something bad happens to his one.

Thanks to everyone who has contributed to this thread - I've learned a lot about BIAB while looking into it - and I obviously have to keep Fast Generation switched off.

I still think there's a problem with the underlying Fast Generation code which has been revealed, not caused, by my slower machine. If the "Next" button is pressed after a song has started but before the generation is complete (or the equivalent in JukeBox), BIAB doesn't tidy up properly before starting on the next song, and trips itself up.