Potatoes not flowering, should i harvest?

Not all potatoes flower.  I've got 5 varieties and only one has flowers on it.  In terms of readyness, you're looking at minimum of 16 weeks for first earlies but if you don't know what variety it is, that information is no use.  I usually try and wait until the tops start to keel over but if you're feeling impatient lift one.  If they're not what you expect in terms of size, you'll know to leave the rest a bit longer.  I'm currently sitting on my hands and trying to resist peeking at mine.  They went in round the same time as yours but we had a big frost late on and I'm concerned it will have put them back a couple of weeks.

I have grown some nice spuds this year and only seen two plants out of 54 with a flower on them ??