This is a hybrid between Nepeta racemosa and Nepeta nepetella which is supposed to be sterile. Being of garden origin the assumption would reasonably be that plants survive as throw-outs but this one was in an unlikely place in the middle of a dune system.

It's not obvious how this plant gets around into the countryside as it is found dotted throughout England, Scotland and Wales but with very little in Ireland. Perhaps as Stace suggest some it is incorrectly identified and actually is Nepeta racemosa.