I set the TempoTrainer for my 'fast lengths' and for the first set and perhaps the second, I managed to do 3x100m at a sub 2:00min/100m pace. I suspect that for sets 3 and 4 I didn't achieve this. Unfortunately I couldn't transfer the data when I came home.
Moreover today's swim didn't appear in the history. That's a little irritating but I know that I put in the training effort and ultimately that's more important than the data. The ANT+ only interface on the Garmin Swim seems to make it hard to do transfers manually, at least I couldn't find anything about it online. Having accepted that today's swim was lost I've done a hard reset on the watch in case something was 'confused', better to start afresh than risk the loss of new data.