I am posting this as a new query so it doesn't get lost in Folkieboater's original post.
Further to Iannodetruffe's response, thank you by the way, it looks a good tool, it says that my VO2-max training pace is 7.06 mins/km, it also suggests running at 6 x 800 metres at VO2-max pace with 4 to 6 minutes of recovery jogging between efforts - I wondered how do we know what pace we are running at when not running a whole km?
I have a Garmin (most basic version) so I can see when I've run 800 metres, does the Garmin tell me the pace when it is less than 1km?
TBH no idea why I'm asking as there is no way I can run at that speed anyway, but it must be worth a try.