The earlies, if planted at the end of march, should be ready now, dig one up and have a look. Maincrop will not be ready till the end of august/ september.
I agree with Fred, although I tend to wait until the foliage starts dying back. I also lift and use the earlies as I need them, which I've started to do this week. Maincrop ones can all be lifted at the same time as they will store okay.