Maincrop Edwards flowering early

I planted my maincop potatoes - King Edwards - on 1st of May. I tried 'earthing up' as much as I could, but they are now pretty tall, 2 feet plus, and a few actually have flower heads on them.
They are in a very well prepared section of my small veg plot - lots of manure Autumn/Spring but I would not have expected them to be so big after just a few weeks.
Then again, maybe they are not and I am misreading signs. It's the flower heads that are throwing me. This is only me 2nd time planting potatoes, but last year really got me hooked.
Don't worry, I have no intention of lifting them till September. But, it is worrying as to what height they will eventually be.

Comments anyone?