Another neat little unwritten & definitely unadvertised rule they run at Heathrow is that even if you have duty free in a clear double sealed plastic bag with the time & date stamped receipt clearly visible, if you're not transiting from a European airport it's liable to be confiscated.
Thankfully in this case I was able to go back land side, check in a bag that came with the duty free & wrap my duty free in some clothes that we had to change mid-way to freshen up. Shockingly, it actually survived the trip in the hold up to Edinburgh.