Nettles are around in two forms at this time of the year:
a) Uncut plants which will have gone to seed and which will be tough and inedible.
b) Plants which have been cut down in the last couple of months and have sprung up again from the base. These will probably be tender and edible (though I have many I have never tried them). They will be blackened by the frost and will die, to emerge next spring.
I see your recipe http://www.bbc.co.uk/food/recipes/winte ... hest_73076
comes from Greg Wallace, who was a greengrocer and probably is still accustomed to things coming from the market, rather than knowing much about them in the wild.
If you are keen on the freshness of spring nettles, have a go next year at my soup recipe:viewtopic.php?f=7&t=6756