Thanks everyone...
So to update, the cheese was safely allowed through security (I thought I was going to have it confiscated...the precious jar had cracked, and the smell was serious! But no, it was allowed through...perhaps because of the smell
On the Harrods airside option, they haven't stocked said cheese for some time...it used to be an option, but there's no chilled foods available now.
Saying all that, we have now discovered Fortnum & Mason online...Mrs NWSRG is happy with that! (Shopping way above our means, but sure, it's Christmas