I was Googling 'gluten free Marmite' when I came across this update - admittedly from 2014
coeliac.org.uk/about-us/new...
However, Meridian do a gluten free yeast extract if you want to play it safe:
hollandandbarrett.com/shop/...
Not having had any for about three years, and loving the stuff, I'm off to Holland and Barrett for the g.f. version.