Vapour control layer

[MorrisWoodman12]

I want to put a 25mm layer of Celotex insulation into the floor of my workshop. Currently the floor comprises a concrete base, an engineered laminate flooring plank (resin impregnated?) ('cos I have loads) topped with a damp prrof membrane. On top of that are the wooden floor bearers with the pine floorboards nailed down to them. The Celotex will sit on top of the floorboards and then the whole topped off with more laminate flooring. There is plenty of ventilation blow the floorboards.
My question to those who know better than I is: should I fit a vapour control layer and, if so, then should it be either above or below the Celotex?
Thanks.
Martin